c1c8 hydrocarbons in sediments from guaymas basin gulf of california comparison to peru margin japan trench and california borderlands surface seafloor sediments hydrothermal vent samples and deep sea drilling project sediments hole 481a from the guaymas basin were examined for c1c8 hydrocarbons the proportions of various classes of compounds were examined and compared to those from other geographic areas peru upwelling region and japan trench to gain insight into the relative importance of thermal generation migration and biodegradation concentrations of c2c7 hydrocarbons were about 10 10 000 times higher in geothermally warm estimated to have been exposed to maximum temperatures in the range of 30 150 c guaymas basin sediments in comparison to the low concentrations 0 1 10 ppb per compound typical of geothermally cold maximum thermal exposure less than 20 c seafloor and dsdp diatomaceous sediments however one sediment sample from dsdp site 477 estimated to have been exposed to temperatures of 300 c or higher in the past showed only a limited hydrocarbon composition consisting of c1c3 alkanes and aromatic hydrocarbons only alkene alkane ratios of 0 1 or greater were typical of both geothermally cold sediments and also of very hydrocarbon richalvin samples recovered from the seafloor because little or no alkene was generally detected in buried sediments exposed to geothermal temperatures greater than 30 c it is suggested that the alkenes are produced by biogenic processes normal alkenes predominated over cyclic and branched structures in geothermally cooler 20 c sediments with the proportion of cyclic and branched compounds increasing in hotter sediments concentrations ofgem dimethyl and aromatic compounds generally remained approximately constant or increased slightly with temperature in comparison with geothermally cold shallow sediments similarities in compositions of branched and cyclic compounds were observed in some pairs of bitumen rich guaymas seafloor samples recovered from different areas suggesting common mechanisms of light hydrocarbon generation and or migration localized increases in ratios of specific cycloalkane ratios were observed adjacent to sill intrusions

are granitic intrusions scale invariant published length l and thickness t data on 135 laccolith and 21 granite intrusions define power law relationships of the form l kt a typical of systems exhibiting scale invariant fractal behaviour both data sets are characterised by an exponent a 1 0 88 0 1 for laccoliths and 0 80 0 20 for plutons that reflects an inherent preference for scale invariant tabular sheet geometries these power law size relationships can be explained in mechanical terms by the need for an incoming magma sheet to travel laterally some distance before vertical thickening can occur sheet thickness is a function of available magma pressure which for an intrusion fed by a feeder dyke is proportional to the vertical magma transport distance

diagenetic clay mineral composition as a function of pressure temperature and chemical activity abstract electron microprobe analyses are made together with x ray diffraction determinations of diagenetic mixed layer clays which have an r3 type structure and are found in two jurassic sandstone units of the north sea viking graben higher and more variable smectite content 2 12 of more deeply buried layers is attributed to differences in pressure or fluid composition during crystallization diagenesis neither temperature nor whole rock composition seems to have been responsible for the differences in mineralogy found it is necessary to consider not only the possible effects of temperature on clay mineral solid solution series such as the illite smectite mixed layer clay but also those of pressure lithostatic versus hydrostatic and aqueous solution composition

light hydrocarbon gases in guaymas basin hydrothermal fluids thermogenic versus abiogenic origin light hydrocarbon gases methane through pentane in high temperature hydrothermal fluids of the guaymas basin gulf of california are predominantly derived from thermocatalysis of organic carbon in sediments intruded by mid ocean ridge volcanic rocks the spectrum of c1 c5 gases in guaymas basin hydrothermal fluids is characterized by a preponderance of alkanes with essentially no alkenes present comparison with high temperature fluids from 21 n on the east pacific rise where geochemical evidence indicates a distinct lack of thermogenic gas and where methane is derived abiogenically from the basalts shows that the 21 n hydrocarbon gases are characterized by a prominent ethylene signature stable isotope compositions of guaymas basin m thane differ from 21 n gas guaymas basin has dgr13c values of 43 to 51 pmil vs pdb compared to 21 n where values as high as 15 pmil have been measured these differences reflect the different origins of light hydrocarbon gases in the two systems with guaymas methane being overwhelmingly of an organic thermogenic derivation and showing no evidence of the abiogenic basalt derived gas that characterizes the 21 n environment carbon isotope analyses of dissolved inorganic carbon in guaymas basin hydrothermal fluids indicate that high temperature hydrocarbon oxidation may be an important process acting in conjunction with high temperature thermocatalytic hydrocarbon generation

predictive mapping of prospectivity and quantitative estimation of undiscovered vms deposits in skellefte district sweden mapping of mineral prospectivity and assessment of undiscovered mineral deposits both aim to delineate prospective ground for mineral exploration but the latter is usually carried out exclusive of the former we propose that the spatial distribution of known mineral deposits of the type sought is the key to link mapping of mineral prospectivity and assessment of undiscovered deposits we demonstrate this proposition in regional scale mapping of prospectivity for volcanogenic massive sulphides vms deposits and estimation of undiscovered vms endowment in the skellefte district sweden the results of analyses of the spatial distribution of known vms deposits and their spatial associations with geological features are consistent with existing knowledge of geological controls on vms mineralization in the district and we used them to define spatial recognition criteria of regional scale vms prospectivity integration of layers of evidence representing spatial recognition criteria of vms prospectivity via application of data driven evidential belief functions results in a regional scale map of prospective areas occupying 15 of the district and having fitting and prediction rates of 100 we used the map of prospective areas and proxy measures for degrees of exploration based on the spatial distribution of known vms deposits in one level prediction of undiscovered mineral endowment we obtained estimates of 709 kt undiscovered cu endowment 3190 kt undiscovered zn endowment 95 mt undiscovered ore tonnage and 48 undiscovered vms deposits these estimates are slightly ca 5 on average lower than and thus corroborated by estimates obtained via radial density fractal analysis of the spatial distribution of known vms deposits therefore mineral prospectivity mapping can be a part of mineral resource assessment if the spatial distribution of discovered deposits of the type sought is considered in both predictive modeling processes

comparison of 14c ages of hydrothermal petroleums abstract in order to set limits on the time frame of formation of hydrothermal petroleum we have obtained 14 c ages on samples from three diverse regions gulf of california guaymas basin northeast pacific ocean escanaba trough and middle valley and the east african rift tanganyika trough the results date the source of carbon and therefore provide maximum ages for the formation and emplacement of the hydrothermal petroleums the youngest petroleum occurs iin the souther trough of guaymas basin 3200 6600 yr mean 4692 yr in the northern trough the petroleum is slightly older 7400 yr significantly older hydrothermal petroleum occurs in escanaba trough 17 000 yr and middle valley 29 000 yr a continental example from the east african rift has an age of 25 000 yr comparable to the ages observed in the oceanic samples from the northeast pacific ocean these ages affirm that hydrothermal petroleum formation is a very rapid process and took place some time between the latest pleistocene and the present in these active hydrothermal systems

survey of hydrothermally generated petroleums from the guaymas basin spreading center abstract the guaymas basin spreading center and hydrothermal system are generating an assortment of petroleum like bitumens by pyrolysis of organic matter in the overlying uncosolidated sediments samples collected by d s v alvin from hydrothermal fields in the southern trough exhibit large variations in the quantities and character of the solvent soluble organic materials various pyrolytic regimes combined with fluctuating thermal gradients and migration velocities may impart a compositional fractionation possibly by differential gaseous solubilization and hydrodynamic alteration of the multi component fluids the data suggest that differential condensation solidification biodegradation and water washing cause selective removal of components at the seabed many hydrothermal oils are unlike normal reservoir petroleums because they contain significant concentrations of polar material due to their rapid genesis and transport and probable solubilization or advection of polar immature components the biomarker distributions confirm high temperature pyrolysis at depth with variable entrainment of less thermally mature bitumens during transport data for shallow core samples from the northern trough indicate that those locations experienced variable influx predominantly volatiles of a low temperature pyrolysate

water column anomalies associated with hydrothermal activity in the guaymas basin gulf of california abstract sea floor hydrothermal activity in the guaymas basin gulf of california is quite different from that associated with ridge crest spreading centers injection of hydrothermal fluids occurs in the bottom of a semi enclosed basin and water column anomalies produced by this activity increase to much higher values than in the open ocean in the guaymas basin the hydrothermal venting generates large clouds of fine suspended particulate matter spm 100 300 m above active mounds and chimneys these hydrothermal clouds have potential temperature anomalies of about 0 010 0 020 c are enriched in dissolved silica particulate manganese and depleted in dissolved oxygen relative to areas away from the vents the particulate manganese values increase from about 3 nmol kg at 1000 m well above the enclosing topography of the subsill basin to 100 150 nmol kg in the clouds of spm and in the bottom nepheloid layer the particulate mn in the hydrothermal clouds appears to originate from both direct precipitation of dissolved mn2 injected by the vents and entrainment of mn rich spm in the rising hydrothermal plumes injection of silica rich vent fluids into the basin bottom waters produces a silica anomaly of 10 15 mol relative to the other deep basins of the gulf of california spillover of guaymas basin deep water produces a silica plume just above the basin sill depth which is detectable to the mouth of the gulf a simple two endmember mixing model indicates that the deep waters of the guaymas basin contain approximately 0 1 hydrothermal fluid oxygen anomalies associated with the hydrothermal clouds are on the order of 5 mol relative to regions away from active vents the basin as a whole shows a depletion in oxygen of about 13 mol relative to the other deep basins of the gulf the mixing model shows that this oxygen consumption can be explained by the oxidation of dissolved sulfide and methane injected by the hydrothermal vents box models of the deep basins of the southern gulf of california indicate that the guaymas basin has a significantly higher source term for dissolved silica and sink term for dissolved oxygen than the other basins the calculated flux of hydrothermal fluids into the guaymas basin is 10 12 m3 s

local to regional scale structural controls on mineralisation and the importance of a major lineament in the eastern mount isa inlier australia review and analysis with autocorrelation and weights of evidence although major crustal lineaments may play an important role in mineralisation the relationship between lineaments and mineral deposits can be quite cryptic and structural controls may vary as a function of scale along lineaments major lineaments alone may be of limited use for detailed target generation the cloncurry lineament in the eastern part of the mount isa inlier is a crustal scale structure defined by potential field derived worms weights of evidence quantifies the association between mineral occurrences and this lineament autocorrelation is used to recognise structural controls on mineralisation at different scales by progressively limiting the lengths of the vectors between mineral occurrence points in the autocorrelation plot the weights of evidence analysis shows that au au cu cu au and cu deposits have a positive spatial correlation to the cloncurry lineament which suggests it that acted as a primary crustal scale control on the localisation of cu and au through focussing mineralisation systems on a broad scale however autocorrelation defines a variety of local structural controls which can be interpreted as shear zones variably oriented fault sets en echelon fault arrays and potentially the orientation of bedding and or iron formations which localise fluid flow and mineral deposition at finer scales the results suggest that major lineaments defined by geophysical contrasts can be used in conjunction with techniques of spatial analysis for targeting structurally controlled mineralisation in areas under thin cover adjacent to mineralised terrains such as the mt isa inlier

hydrothermal petroleum genesis migration and deposition in guaymas basin gulf of california hydrothermal activity and seabed mounds have been explored in guaymas basin by the deep sea drilling project dsdp piston coring dredging and diving with the deep submersible research vessel dsrv alvin sedimentary organic matter derived primarily from immature degraded microbial detritus is easily converted to petroleum under the hydrothermal regime these petroleums are mature and migrate in the fluids and by diffusion to the seabed the fluid migration is aided by near critical aqueous solution and supercritical carbon dioxide and hydrocarbons petroleum compositions vary from condensates to naphthenic to waxy all with significant amounts of asphaltenes and hydrothermal products such as olefins and toxic polynuclear aromatic hydrocarbons pah the heavy ends condense at the seabed depositing mainly as a cement with the sulfides and other minerals and to a lesser extent as entrapped oil and crystalline wax in vugs and conduits of the mounds the pah are high temperature resynthesis aromatiza

ore controls in the charters towers goldfield ne australia constraints from geological geophysical and numerical analyses the approach taken in this paper namely synthesising a wealth of previous information with new data and a genetic model in combination with integrated numerical analyses led to new insights into the geological controls on the localisation of auriferous veins and residual prospectivity of the charters towers goldfield ne australia the method also has implications for the assessment of other mature goldfields worldwide despite a number of different ore controls having operated within the charters towers goldfield the controlling factors can be linked to a single genetic model for orogenic granitoid hosted lode gold mineralisation in a brittle deformation regime d4 of ne sw to nne ssw shortening under conditions of supralithostatic fluid pressure and low stress difference spatial autocorrelation results suggest district scale alignment of the auriferous veins parallel to and overlapping with the ese wnw to e w striking charters towers ravenswood lineament a major crustal boundary in the basement to the ravenswood batholith at the camp scale auriferous veins have abundance and proximity relationships with nw se nnw sse ne sw and ene wsw oriented lineaments suggesting that structures that controlled gold deposition in one camp did not necessarily control mineralisation in other camps fractal dimensions obtained with the box counting method range from 1 02 to 1 10 whereas veins in the charters towers city camp are characterised by a significantly higher fractal dimension of 1 28 this discrepancy may be taken to imply that most or all outcropping and near surface deposits within the charters towers city camp have been found and that new discoveries are more likely to occur at greater levels of depth or outside the boundaries of this camp the new understanding has implications for the assessment of the residual prospectivity of the charters towers goldfield where large areas of prospective rock types and structures e g approximately 40 of the charters towers ravenswood lineament are hidden under cover this parameter space was inaccessible to the historic prospectors and has received relatively little attention from recent explorers the following steps are suggested for the development of a targeting strategy for lode gold exploration in areas of the goldfield under cover 1 identify from geological and geophysical data the ene wsw 15 and nnw sse 15 striking structures and geological boundaries within a 20 km wide corridor parallel to and centred upon the charters towers ravenswood lineament the potential control on gold deposit distribution at the regional to district scale 2 interpret from geological and geophysical data the distribution of pre middle devonian granitoids within these areas that are the preferred host rocks of the payable gold deposits 3 deduce from geophysical data the ene wsw 15 and nnw sse 15 striking structures that cut or bound the intrusions identified in step 2 4 locate segments along the structures identified in step 3 that deviate most from the geometry of a straight line e g potential bends or splays and or intersect other structures or geological contacts or both and 5 define and rank potential targets within the prospective areas identified in step 4 and systematically test the best ones

fractal geometries of vein systems and the variation of scalingrelationships with mechanism abstract investigation of vein geometries has identified empirical relationships which allow extrapolation of outcrop scale observation to larger scales measurements of vein shapes and aspect ratios in a number of different environments demonstrate that veins follow similar empirical scaling laws to those of faults geometries of veins are easier to characterise accurately than faults because their thickness is related to the variation in displacement from zero at their tips to a maximum at their thickest point vein sizes obey the empirical relationship l kta where l length in mm t thickness in mm 20 1 this suggests that veins amplify initially by inflation and subsequently by elongation

the anatomy of shallow crustal transpressional structures insights from the archaean carajas fault zone amazon brazil abstract the carajas fault zone cfz is the most prominent structure in the e w trending carajas strike slip system casss an ancient upper crustal fault network of probable late archaean age that cuts across the precambrian amazonian craton in brazil the subvertical faults reactivated pre existing high grade basement shear zone fabrics itacaiunas shear zone and display a complex long lived history of movement 1 ga dominated by oblique and strike slip displacements a postulated early regional phase of dextral movement downfaulted units of low grade to unmetamorphosed basement rocks into dilational bends and offsets in the casss subsequent sinistral transpression ca 2 6 ga led to faulting and folding during partial inversion of the cover rocks in these dilational sites with much of the associated deformation focused in the immediate vicinity

petroleum characteristics of the oil in a guaymas basin hydrothermal chimney abstract extensive petroleum shows have been sampled from the seabed of guaymas basin these petroleums were generated at depth by hydrothermal activity from immature sedimentary organic matter and migrated to the sea floor there the heavy ends solodify due to the temperature drop and the volatiles are emitted as plumes thus it is of interest to determine the petroleum characteristics of such oils for comparison with normal reservoir petroleums an oil saturated sample of a chimney alvin dive 1630 emitting water at 200 c was studied in contained 21 7 solvent extractable oil and 19 2 s moisture the oil has an api gravity of 27 6 a specific gravity at 20 c of 0 8891 and contains 0 99 s the astm distillation yields vol are gasoline 3 0 ibp 149 c ibp 300 f intermediates 149 315 c 300 660 f 61 0 gas oil 315 538 c 660 1000 f 21 0 and residue 538 c 1000 f 15 0 gas chromatography and ft infrared spectrometry indicate that this oil is similar to typical reservoir petroleum but with the low ends and aromatics depleted due to water washing mild thermal conditions are indicated by the absence of cracking products

fractals in geology and geophysics the definition of a fractal distribution is that the number of objectsn with a characteristic size greater thanr scales with the relationn r d the frequency size distributions for islands earthquakes fragments ore deposits and oil fields often satisfy this relation fractals were originally introduced by mandelbrot to relate the length of a coastline to the length of the measuring stick this application illustrates a fundamental aspect of fractal distributions scale invariance the requirement of an object to define a scale in photographs of many geological features is one indication of the wide applicability of scale invariance to geological problems scale invariance can lead to fractal clustering geophysical spectra can also be related to fractals these are self affine fractals rather than self similar fractals examples include the earth s topography and geoid

a time series of vent fluid compositions from 21 n east pacific rise 1979 1981 1985 and the guaymas basin gulf of california 1982 1985 a time series study of four hot spring fields at 21 n on the east pacific rise demonstrates that the solution compositions of mid ocean ridge hydrothermal vents are stable on a decadal time scale the ocean bottom seismometer obs national geographic smoker ngs and south west sw vents show no significant changes in the major element composition of their end member fluids since 1979 two of the vents obs and sw have maintained exit temperatures near 350 c since 1979 the ngs vent has remained close to 270 c since 1981 after cooling from 350 c in 1979 only one vent hanging gardens shows important changes in solution chemistry from 1981 to 1985 in 1985 this vent appears to have cooled 10 c relative to the other vents the depth of the reaction zone as determined by quartz geobarometry has increased by about 1 km at this vent the large fluxes of compositionally stable fluids from these vents cannot be explained by transient conditions and unique circumstances rather the constancy of small interfield variations in solution composition is more consistent with control by rock buffering a 4 year time series study of hydrothermal vents in the guaymas basin also shows no significant changes in the major element composition of the end member fluids interfield differences in solution chemistry have been maintained from 1982 to 1985 this phenomenon is best explained in terms of an equilibrium model

deep water hydrocarbon seeps in guaymas basin gulf of california abstract acoustically discovered hydrocarbon seeps along a transform fault zone on the sonoran margin of guaymas basin and in the southern trough of guaymas basin were examined and sampled during dives of dsv alvin seepage of methane and heavier hydrocarbons occurs through shallow pockmarks along the eroding crest of a steep anticline 1600 m below sea level extensive ledges of aragonite crop out around the rims of the pockmarks isotopic analysis indicates that carbonate precipitation is a result of methane oxidation seepage zones within the pockmarks support dense communities of calyptogena half buried in the mud tubeworms lamellibracheae sp have colonized many of the aragonite outcrops though the margin site is only a few kilometers from a high temperature sulfide precipitating and petroleum discharging vent system at a nearby center its structural setting is more akin to pockmarks described from continental shelves and its chemosynthetic fauna is more like that around low temperature seeps on other continental slopes and margins e g oregon u s a and japan the seep in the southern trough is a condensate type petroleum c 1 c 40 and rises as a plume from a young vent mound system about 2000 m below sea level

liquid hydrocarbon bearing inclusions in modern hydrothermal chimmeys and mounds from the southern trough of guaymas basin gulf of california abstract liquid hydrocarbon bearing inclusions of variable shape e g spherical bowling pin rod and highly irregular occur in hydothermal minerals of chimneys and mounds in the southern trough of guaymas basin central gulf of california the inclusions are preferentially trapped in amorphous silica which occurs as spherules and 0 01 mm thick encrustations on sulfides sulfates and carbonates the inclusions are primary and pseudosecondary and were trapped during not after mineral growth the inclusions are both two phase liquid hydrocarbon and vapor gas and three phase liquid hydrocarbon aqueous fluid and vapor and range from 2 to 50 m in diameter the large range in liquid hydrocarbon and acqueous fluid contents indicates that the hydrothermall fluid and liquid hydrocarbon were never a homogeneous solution but that hydrocarbons were transported as immiscible and possibly solvated forms the liquid hydrocarbon varies in color from deep to pale orange brown and fluoresces a yellow color during excitation by u v light indicating a condesate mainly c 1 to c 10 hydrocarbons composition measurable quantities of hydrocarbons from the inclusions could not be isolated by mineral dissolution by pyrolsis and decrepitation analyses suggest that the more volatile components predominate two phase hydrocarbon inclusions homogenized with the liquid at temperatures ranging from 75 to 190 c excluding one high measurement to obtain true trapping temperatures an unknown pressure correction is required however the trapping temperature of these hydrocarbon inclusions was estimated by measuring trapping temperatures for adjacent aqueous inclusions which range from 116 to 226 c geochemical modelling using these trapping temperatures indicates that the amorphous silica precipitated from the hydrothermal fluid due to conductive cooling in addition to mixing with ambient sea water the temperatures required for the formation of petroleum and its transport to the seafloor in the guaymas basin coincide with those necessary for the precipitation of amorphous silica in the guaymas basin hydrothermal system

mercury isotopic composition of hydrothermal systems in the yellowstone plateau volcanic field and guaymas basin sea floor rift abstract to characterize mercury hg isotopes and isotopic fractionation in hydrothermal systems we analyzed fluid and precipitate samples from hot springs in the yellowstone plateau volcanic field and vent chimney samples from the guaymas basin sea floor rift these samples provide an initial indication of the variability in hg isotopic composition among marine and continental hydrothermal systems that are controlled predominantly by mantle derived magmas fluid samples from ojo caliente hot spring in yellowstone range in 202hg from 1 02 to 0 58 0 11 2sd and solid precipitate samples from guaymas basin range in 202hg from 0 37 to 0 01 0 14 2sd fluid samples from ojo caliente display mass dependent fractionation mdf of hg from the vent 202hg 0 10 0 11 2sd to the end of the outflow channel 202hg 0 58 0 11 2sd in conjunction with a decrease in hg concentration from 46 6 pg g to 20 0 pg g although a small amount of hg is lost from the fluids due to co precipitation with siliceous sinter we infer that the majority of the observed mdf and hg loss from waters in ojo caliente is due to volatilization of hg0 aq to hg0 g and the preferential loss of hg with a lower 202hg value to the atmosphere a small amount of mass independent fractionation mif was observed in all samples from ojo caliente 199hg 0 13 1 0 06 2sd but no significant mif was measured in the sea floor rift samples from guaymas basin this study demonstrates that several different hydrothermal processes fractionate hg isotopes and that hg isotopes may be used to better understand these processes

analysis of the fractal clustering of ore deposits in the spanish iberian pyrite belt the iberian pyrite belt ipb contains one of the greatest known concentrations of volcanic hosted massive sulfides vhms on earth investigation of the spatial attributes of the mineralization using fractal methods over a range of scales and integrated within a gis provides new information of potential import to the exploration of vhms deposits at the mine scale stockworks which act as feeders for hydrothermal fluids show vein thickness distributions that are power law dt 0 65 in one dimension at length scales from about 10 2 to 102 m box counting of veins indicates a capacity dimension dc in the range of 1 60 1 65 in two dimensions which is consistent with the vein thickness data at larger scales in the range 103 to 105 m the distribution of mines and mineral prospects can be modelled as a fractal dust when all the known mineral deposits and prospects are analyzed they have a capacity dimension dc 1 3 the vhms deposits alone have a capacity dimension dc 0 9 indicating that they are clustered with some indication that the world class deposits may be even more clustered the different fractal analyses are integrated with information from geological and geophysical maps using a gis the distribution of prospects has been simulated using a simple multifractal model of the ore concentration and is constrained by known geological controls such a model has been implemented through the gis

hydrothermal petroleum in mineralized mounds at the seabed of guaymas basin petroleum has been dredged from an active hydrothermal mound area in the southern rift of guaymas basin gulf of california this organic matter is composed of gasoline range aliphatic and aromatic hydrocarbons and predominantly residual polar asphaltic material the aliphatic hydrocarbons of two bitumen samples have very different boiling range and composition both samples contain polynuclear aromatic hydrocarbons and olefins which indicate formation at pyrolytic temperatures the overall compositional data indicate an origin from biological detritus by thermal alteration and rapid quenching by hydrothermal removal followed by condensation at the seabed

organic geochemistry of deep sea drilling project sediments from the gulf of calofornia hydrothermal effects on unconsolidated diatom ooze abstract the effects of intrusive thermal stress have been studied on a number of pleistocene sediment samples obtained from leg 64 of the dsdp ipod program in the gulf of california samples were selected from sites 477 478 and 481 where the organic matter was subjected to thermal stress from sill intrusions for comparison purposes samples from sites 474 and 479 were selected as representative of unaltered material the gc and gc ms data show that lipids of the thermally unaltered samples were derived from microbial and terrestrial higher plant detritus samples from sill proximities were found to contain thermally derived distillates and those adjacent to sills contained essentially no lipids curie point pyrolysis combined with gc and gc ms was used to show that kerogens from the unaltered samples reflected their predominantly autochthonous microbial origin pyrograms of the altered kerogens were much less complex than the unaltered samples reflecting the thermal effects the kerogens adjacent to the sills produce little or no pyrolysis products since these intrusions into unconsolidated wet sediments resulted in in situ pyrolysis of the organic matter examination of the kerogens by esr showed that spin density and line width pass through a maximum during the course of alteration but esr g values show no correlation with maturity stable carbon isotope 13 c values of kerogens decrease by 1 1 5 near the sills at sites 477 and 481 and the atomic n c decreases slightly with proximity to a smaller sill at site 478 differences in maturation behavior between site 477 and 481 and site 478 are attributed to dissimilarities in thermal stress and to chemical and isotopic heterogeneity of guaymas basin protokerogen

influence of a turbidite deposit on the extent of pyritization of iron manganese and trace metals in sediments from the guaymas basin gulf of california mexico abstract a core collected in the guaymas basin contained an organic poor mn oxide rich and relatively fe oxide rich turbidite layer that affected the distribution of fe mn c s and trace metals results indicate that sediments not influenced by the turbidite layer achieved a 100 degree of pyritization and by extension that pyrite production is fe limited in these sediments in contrast the mud slide layer apparently supplied enough reactive fe to transfer essentially 98 of the total s present at the base of the turbidite 17 19 cm to the pyrite reservoir c s ratios showed rapid decreases with depth from a high of 38 close to the sediment water interface to minimum values of 2 8 at the lower limit of the turbidite layer a ratio equal to the average c s value of normal marine modern sediments where concentrations of organic c and pyrite supposedly have attained quasi steady values a significant part of the reactive mn was associated with carbonates 41 12 and to a much lower degree with pyrite 2 7 1 2 the turbidite layer is currently showing a depletion of mn relative to the host sediment it is possible that mn a major metal constituent in these sediments was initially present in high concentrations in the mud slide but was eventually mobilized and transferred either to the water column or to the sediments immediately below the turbidite layer metals associated with this element probably followed the same path affecting their incorporation into pyrite the turbidite layer apparently affected the distribution of most of the trace metals associated with pyrite except maybe cd pb and to a certain extent cr however cu cr zn ni and co were all found to be highly pyritized 80 in the sediments of the guaymas basin

programmed pyrolysis of organic matter from thermally altered cretaceous black shales organic rich cretaceous black shales from the cape verde rise in the eastern atlantic were penetrated by hot diabase sills during the miocene programmed pyrolysis and pyrolysis gas chromatography of organic matter from core samples taken at various distances from a major sill were used to show 1 the type of kerogen 2 its relative level of thermal maturity 3 the fraction of pyrolyzable organic compounds which are free and 4 the compositions of the bitumen and kerogen the dominant factor affecting these sediments appears to be thermal maturity rather than differences in the quality of the organic matter systematic changes in the pyrolyzate resulted from thermal cracking of volatile organics from the oil prone type ii kerogen generation of these products caused progressive aromatization of the residual kerogen closer to the sill these conclusions are supported by changes in kerogen elemental compositions quantity of bitumen extract and vitrinite reflectance although the major sill is 15 m 50 ft thick solvent extraction and pyrolysis results show that hydrocarbon generation was restricted to within about 10 m 33 ft of the shale sill contacts at equal distances the maximum temperature reached by the shales was higher above than below the sill the reflectance of vitrinite responds more rapidly than bitumen composition to high temperatures imposed over a short time

heat flow hydrothermal circulation and basalt intrusions in the guaymas basin gulf of california abstract the guaymas basin is part of an en echelon series of short seafloor spreading segments in the gulf of california the basin is separated from adjacent deeps by long northwest southeast striking transform faults and divided into subparallel northern and southern troughs which trend northeast to southwest rapid sedimentation 1 to 5 m ka 1 results in a striking morphological contrast between seafloor spreading in the guaymas basin and that in more mature mid ocean settings basalt does not extrude onto the seafloor in the basin as flows and pillows but instead intrudes into a thick sediment layer the presence of relatively unconsolidated sediments lining the floor of the basin make this setting ideal for the study of axial heat flow and the thermal budget of oceanic crustal formation thermal data delineate several modes of heat transfer in both troughs of the basin with negligible heat flow in some areas and values greater than 3 w m 2 in others broad heat flow highs several square kilometers in area result from a combination of deep conductive heat flow slow intergranular fluid circulation and vigorous hydrothermal venting areas of low heat flow between heat flow highs and near normal faults which bound the basin may be indicative of hydrothermal recharge the geometry of faults shallow sills and broad northeast southwest structural trends in the basin largely seems to govern the distribution of heat flow the highest values are clustered within a few isolated zones in each trough with a total area of about 30 km 2 variations in heat flow of two orders of magnitude occur over distances as small as a few hundred meters fourteen hydrothermal vents in the southern trough of the guaymas basin have been sampled directly and found to have temperatures in excess of 250 c locally conductive heat flow at the seafloor is significantly raised in the vicinity of these vents but the general pattern appears to require more deeply seated conductive heat sources the mean heat flow in the southern trough is 453 342 s d mw m 2 a simple analysis of the heat budget in the southern trough suggests that the total intruded section between the top of the magma chamber and the seafloor may be unusually thin perhaps only several hundred meters in thickness

spatial distribution of ore deposits conventional spatial distributions such as the negative binomial and neyman scott have been proposed as models for the clustered distribution of ore deposits b b mandelbrot has proposed that ore deposits are clustered at many different scales and that fractal distributions are appropriate the apparent fractal characteristics of geologic controls on the locations of hydrothermal deposits self similar systems of fractures circulation cells and magmatic intrusions support his proposal examination of the spatial distribution of 4775 hydrothermal precious metal deposits in the basin and range western united states reveals fractal distributions acting within two scale ranges together covering the entire range from 1 to 1000 km this result gives additional credibility to concepts of regional controls on mineralization such as metallogenic provinces and tectonostratigraphic terranes the distribution of these ore deposits about a known occurrence follows a regular radial density law within a range of radii r of 1 to 15 km the probability density function of these deposits is given by d 0 46 r 1 17 and within a range of radii of 15 to 1000 km by d 0 08 r 0 83 where d is deposits per square kilometre

hydrothermal pyrolysis of organic matter in guaymas basin i comparison of hydrocarbon distributions in subsurface sediments and seabed petroleums abstract the bitumens of a selection of subsurface sediments from guaymas basin gulf of california have been analyzed in order to assess the hydrothermal effects on the organic matter and to better delineate the processes influencing the generation deposition and alteration of the hydrothermal petroleums at the seabed although the thermally generated subsurface bitumens are generally rich in polar asphaltic materials as are the seabed oils the hydrocarbon transformations parallel the extent of hydrothermal alteration as reflected in the downcore mineralogy at dsdp sites 477 and 478 at site 477 a progressive change from n alkane to aromatic hydrocarbon dominated patterns in the high resolution gas chromatography resolvable fractions of the bitumens accompanies decreases in organic carbon and bitumen yields with depth these transformations are indicative of sequential hydrothermal alteration of the sediments with depth due to increasing temperature and or progressive passage of hydrothermal fluid through the sedimentary column the polycyclic aromatic hydrocarbon pah distributions undergo extensive transformations e g dealkylation consistent with hydrothermal alterations are dominant at depth and have the broadest range as thermal maturation indices the aliphatic and aromatic components of the seabed oils can be transported to the seabed independently as a result of their generation under different temperature or depth regimes and sequentially over time during pyrolysis the concentrations of the parent pah in the thermally altered subsurface bitumens are comparable to those in the seabed oils the differential dissolution of the more soluble aromatics and selective solidification condensation of the higher molecular weight pah out of the high temperature fluids exiting at the seabed chimneys result in aromatic distributions of the oils significantly skewed towards the larger components e g benzo ghi perylene relative to the subsurface bitumens comparison of the downcore hydrocarbon distributions with those in the seabed petroleums support the contention that the hydrothermal oils are mixtures of pyrolysates from different depths or thermal regimes and are significantly altered by differential solubilization during transport and at the seabed

geochemistry of shallow sediments in guaymas basin gulf of california hydrothermal gas and oil migration and effects of mineralogy offset of prograde hydrothermal alterations by retrograde reactions is evident in sediments from a piston core pc6 8 m long from the guaymas basin gulf of california geochemical and mineralogical analyses of sediments and pore fluids show superimposed geochemical signals that indicate currently active reactions are modifying previously formed secondary solids hydrothermal barite was formed in a previously active flow channel between 150 and 250 cm depth hydrothermal gypsum is presently dissolving at depths 780 cm below which hydrothermal fluid flow is channeled by a secondary dolomite layer thermal stress of organic matter generates hydrothermal gas and petroleum having wide ranges of compositions and maturities a significant amount of hydrothermally generated oil has been transported laterally through a porous debris flow approx 240 cm subbottom overwhelming the indigenous bituminous matter water soluble petroleum constituents have disseminated throughout the cored sediments from 400 to 700 cm depth the immature organic matter continues to experience thermally enhanced diagenesis and an even higher thermal stress has occurred at the bottom of the core enhanced bacterial degradation of organic matter has led to depletion of pore water sulfate and enrichment of ammonium nh4 in both pore fluid and sediment resulting in formation of nh4 bearing secondary clay minerals at depths below 780 cm

evidence for retrograde hydrothermal reactions in near surface sediments of guaymas basin gulf of california abstract the guaymas basin gulf of california is a sediment covered portion of the east pacific rise where hydrothermal fluids exit to the sea floor via both direct emanation from spires and chimneys as well as by diffuse circulation through organic matter rich sediments thermal alteration of organic matter generates hydrothermal gas and petroleum which have wide ranges of compositions and maturities diffuse fluid discharge reaches the sediment seafloor interface via channelized pathways that change with time mineralogical and geochemical analyses of sediments and pore fluids from an eight meter long piston core pc 6 show superimposed geochemical signals indicating that presently active reactions are modifying previously formed authigenic materials a slump deposit 140 250 cm shows the presence of hydrothermal barite and a substantially changed chemical composition analysis of the extractable organic matter indicates that a significant amount of hydrothermally generated oil has been transported laterally through the 140 250 cm depth interval overwhelming the indigenous bituminous matter below 782 cm depth sandy layers have undergone substantial hydrothermal alteration as is evident from the presence of gypsum dolomite heulandite well crystallized smectite as well as significant changes in the bulk composition of the solid phases the dolomite layers in the bottom part of the core act as a barrier towards upward fluid flow allowing only diffusive communication with fluids of a hydrothermal origin this is evident from the concentration profiles of dissolved chloride and potassium retrograde reactions e g dissolution of gypsum offsetting prograde hydrothermal reactions in pc 6 sediments illustrate the ephemeral nature of fluid flow pathways in near surface guaymas basin sediments

fractal analysis of seismic and geological data abstract continental lithosphere is a highly organised physical medium which can be investigated by seismic methods to obtain objective information the use of fractal representation offers new possibilities to determine quantitative parameters of the structural arrangement of the lithosphere and to compare tectonic structures composed of a similar set of participants i e structural complexes with a relatively homogeneous range of rocks fractals as a universal property of continental crust are shown to be an important tool for a comparative study of geological and seismic sections on a quantitative basis and also in reassessing many of the previous interpretations of seismic and geological structures

steroid and triterpenoid distributions in bransfield strait sediments hydrothermally enhanced diagenetic transformations abstract recent sediments from bransfield strait antarctica have been analyzed for triterpenoid and steroid hydrocarbons sterols and steroid ketones to consider the effects of hydrothermal fluids on the sedimentary organic matter the steroid distributions in unaltered and altered sediments are controlled more by inputs from source organisms than by the effects of hydrothermal activity which is suggested to be limited to low temperature alteration nevertheless chemical reactions occurred in altered sediments and include dehydration of sterols to sterenes isomerization of triterpenes and sterenes rearrangement of sterenes to diasterenes and reductive processes leading to generation of phytane from phytol via phytenes

spatial analysis of mineral deposit distribution a review of methods and implications for structural controls on iron oxide copper gold mineralization in carajas brazil abstract mineral deposits are formed by interaction of various geological processes and conditioned by controls that favor their formation and preservation the understanding of mineralization controls is critical for mineral exploration because it allows focusing exploration on regions where these controls are concentrated the analysis of the spatial distribution of mineral deposits particularly on a regional scale can provide information relevant to the understanding of regional scale processes involved during their formation here we present a review of fry and fractal methods for spatial analysis of mineral deposit distribution and an application using the iron oxide copper gold iocg deposits of the carajas mineral province brazil results show that different iocg mineralization structural controls acted in scales of 40 km the iocg deposits cluster at scales of

mapping of prospectivity and estimation of number of undiscovered prospects for lode gold southwestern ashanti belt ghana in the southwestern part of the ashanti belt the results of fractal and fry analyses of the spatial pattern of 51 known mines prospects of mostly lode gold deposits and the results of analysis of their spatial associations with faults and fault intersections suggest different predominant structural controls on lode gold mineralisation at local and district scales intersections of nne and nw trending faults were likely predominantly involved in local scale structural controls on lode gold mineralisation whilst nne trending faults were likely predominantly involved in district scale structural controls on lode gold mineralisation the results of the spatial analyses facilitate the conceptualisation and selection of spatial evidence layers for lode gold prospectivity mapping in the study area the applications of the derived map of lode gold prospectivity and a map of radial density of spatially coherent lode gold mines prospects results in a one level prediction of 37 undiscovered lode gold prospects the applications of quantified radial density fractal dimensions of the spatial pattern of spatially coherent lode gold mines prospects result in an estimate of 40 undiscovered lode gold prospects the study concludes finally that analysis of the spatial pattern of discovered mineral deposits is the key to a strong link between mineral prospectivity mapping and assessment of undiscovered mineral deposits

controls on mineral deposit occurrence inferred from analysis of their spatial pattern and spatial association with geological features in this paper point pattern analysis fractal analysis and fry analysis were employed to study the spatial pattern of known occurrences of mineral deposits of the type sought whereas distance distribution method was applied to study the spatial associations between various geological features and known occurrences of mineral deposits of the type sought in the aroroy district philippines the results of the applications of these spatial analytical techniques support a conceptual model of district scale mechanism of geologic controls on low sulphidation epithermal au mineralization which involves a more or less regular mesh of interlinked zones of extension faults fractures at and or around intersections of nnw and nw trending strike slip faults fractures integration of spatial evidential data layers representing these structural controls and surficial geochemical anomalies via knowledge guided application of data driven evidential belief functions results in delineation of prospective areas occupying about 25 of the district in which there is about 70 likelihood of undiscovered occurrences of low sulphidation epithermal au deposits

siliceous sediments of the guaymas basin the effect of high thermal gradients on diagenesis recent siliceous sediments of the guaymas basin a rapid spreading center in the gulf of california are intruded by basaltic sills which induced significant diagenetic and metamorphic changes in the sediments the transformation from opal a to opal ct opal ct to quartz and opal a directly to quartz in these sediments cored on dsdp leg 64 can be used to infer the temperature history and order of emplacement of intrusives at or near contacts with sills of 30 m or greater average thickness opal a inverts directly to authigenic quartz but there is less quartz than would be expected from the amount of opal a dissolution opal ct forms in sediments sandwiched between adjacent sills based on high rates of quartz nucleation and growth at high temperatures 150 c and on considerations of convective solution transfer opal ct is thought to form only where temperatures were lower or at positions between sills an environment which prevents rapid convective dissipation of silica in solution where temper

the connection between iron ore formations and mud shrimp colonizations around sunken wood debris and hydrothermal sediments in a lower cretaceous continental rift basin mecsek mts hungary in the early cretaceous the continental rift basin of the mecsek mts hungary was situated on the southern edge of the european plate the opening of the north atlantic ocean created a dilatational regime that expanded to the southern edge of the european plate where several extensional basins and submarine volcanoes were formed during the early cretaceous epoch permanent seaquake activity caused high swell events during which a large amount of terrestrial wood fragments entered into submarine canyons from rivers or suspended woods which had sunk into the deep seafloor these fragments created extended wood fall deposits which contributed large scale flourishing of numerous burrowing thalassinid crustaceans twelve different thalassinid coprolite ichnospecies can be found in the berriasian hauterivian volcano sedimentary formations

concentration and distribution of trace elements in lignite from the shengli coalfield inner mongolia china implications on origin of the associated wulantuga germanium deposit abstract the wulantuga germanium deposit wgd hosted in coal seams with ge resources up to 1600 mt is located in the shengli coalfield in xilingol inner mongolia china forty two channel samples of ge bearing lignites of the no 6 1 coal seam in lower cretaceous bayanhua formation were collected and analyzed by inductively coupled plasma mass spectrometry icp ms the mode of occurrence of elements in selected lignite samples were studied by cluster analysis and scanning electron microscope with energy dispersive x ray spectrometer sem edx the lignite samples of wgd are distinctly enriched in be ge sb w and u and depleted in rb nb sn and ta compared with the average composition of upper continental crust the average concentrations of above enriched elements also are higher than those of overlying sandstone of wgd and contemporary ge barren lignite of hongqi coal mine in shenli coalfield as well as the average concentration of elements in the usa coals and worldwide coals with an exception of sr most trace elements and ash yields obey the log normal distribution in all 42 lignite samples collected from wgd the elements in these lignites may be classified into four groups the first group ge mo association contains elements with negative correlation coefficients with ash yields and they show mainly organic affinity the elements in the second group tl ga zn co association show negative to moderate correlation coefficients with ash yields and may also have an organic affinity but most of them are mainly related to mineral matter such as sphalerite the last two groups rb cs and w u cd y pb cu hf zr th sn nb ta tio 2 sb ba sr mno be associations contain elements with moderate to high correlation coefficients with ash yields much of them associated mainly with mineral matter such as anatase manganite zircon and barite as identified by sem edx analysis and show mainly aluminosilicate affinity silver bearing particles or native silver were identified by sem edx in the lignites from wgd and hongqi coal mine germanium and mo can concentrate in different proportion of coal seam in different sections while other elements more or less follow the distribution of ash yield the tio 2 normalized elemental profiles reveal that be tio 2 ge tio 2 w tio 2 u tio 2 mo tio 2 sb tio 2 tl tio 2 and sr tio 2 ratios of the lignite samples in three sections of wgd are generally one or two order of magnitude higher than the reference ratios of sandstone from wgd and lignite from hongqi coal mine much more than 90 of these elements be ge w u mo sb tl and sr may be transported into coal seam by solution the ge bearing lignites from wgd are distinctly characterized by lower rb cs ratios higher u th ratios different from those of the overlying sandstone from wgd and contemporary lignite from hongqi coal mine most trace elements in the ge bearing lignite of wgd may have been derived from a granitic source and the enrichment of be ge sb w and u may be attributed to an epigenetic lateral transferred ge bearing solution that leached these elements from the granitic source and transported them into the lignite

the spatial distribution of mineralization applications of fry analysis the spatial distribution of mineralization is a foremost concern in regional exploration research and mine resource assessment here we use fry analysis as a complement to structural geology and geostatistical methods fry analysis uses a geometrical method of spatial autocorrelation for point data for n points there are n 2 n spatial relationships and because of the square function the method yields interpretable results with small as well as large data sets fry analysis is an alternative to variography for directional studies at the regional scale fry analysis can assess distribution patterns of mineralization and potential controlling structures at the deposit scale the characteristics of zones of mineralization such as direction spacing high grade ore direction and grade distribution can all be deduced

hydrothermal discharge and alteration in near surface sediments from the guaymas basin gulf of california abstract in the guaymas basin gulf of california hydrothermal fluids discharge onto the seafloor via both direct emanation through hydrothermal spires and diffusely through the sediments the latter mode is the focus of this study short 20 cm sediment cores were taken in zones of diffuse hydrothermal flow for chemical investigation of interstitial fluids and bulk solids the hydrothermal component of the pore fluids was quite variable indicating the heterogenous nature of the near surface flow regimes the bulk solids chemistry indicates that the suite of cores has encountered different amounts of cumulative hydrothermal exposure dissolution of biogenic silica and deposition of large amorphous silica clasts in the sediment are related to the extent of hydrothermal exposure surface enrichments in ba are formed as barite precipitates when ba rich hydrothermal fluids mix with sulfate rich seawater at the seafloor formation of pyrite and removal of mg from the solid phases are also observed effects of hydrothermal flow through these sediments

tectonic controls on kimberlite location southern africa abstract the relationship between kimberlite the host to diamonds ascent paths from mantle depths 150 km to surface and major structures is controversial we use a geometric method of spatial analysis spadis which requires neither statistics nor algebraic models to show that crustal architecture is critical in the localisation of kimberlites distinct corridors of kimberlites are parallel to but not within prominent shear zones and crustal faults instead the kimberlites occur in relatively homogeneous strong crust capable of maintaining the very high co2 pressures necessary for rapid emplacement archaean directional trends in kimberlite distribution are recognised on craton whereas proterozoic and carboniferous permian karoo age trends are recognised both on and off the archaean craton

lithium isotope geochemistry of sediments and hydrothermal fluids of the guaymas basin gulf of california abstract lithium isotopic compositions of hydrothermally altered sediments of deep sea drilling project dsdp site 477 477a as well as high temperature vent fluids of the guaymas basin have been determined to gain an understanding of lithium exchange during fluid sediment interaction at this sediment covered spreading center unaltered turbidite of the basin has a 6 li value of 10 5 7 heavier than fresh oceanic basalts contact metamorphism induced by a shallow sill intrusion results in a decrease of the lithium content of the adjacent sediments and a lighter isotopic value 8 below the sill sediments altered by a deep seated hydrothermal system show strong depletions in lithium while lithium isotopic compositions vary greatly ranging from 11 to 1 the shift to lighter composition is the result of preferential retention of the lighter isotope in recrystallized phases after destruction of the primary minerals the complexity of the isotope profile is attributed to inhomogeneity in mineral composition the tortuous pathway of fluids and the temperature effect on isotopic fractionation the range of lithium concentration and 6 li values for the vent fluids sampled in 1982 and 1985 overlaps with that of the sediment free mid ocean ridge systems the lack of a distinct expression of sediment input is explained in terms of a flow through system with continuous water recharge the observations on the natural system agree well with the results of laboratory hydrothermal experiments the experimental study demonstrates the importance of temperature pressure water rock ratio substrate composition and reaction time on the lithium isotopic composition of the reacted fluid high temperature authigenic phases do not seem to constitute an important sink for lithium and sediments of a hydrothermal system such as guaymas are a source of lithium to the ocean the ready mobility of lithium in the sediment under elevated temperature and pressure conditions also has important implications for lithium cycling in subduction zones

spatial distribution of kimberlite in the slave craton canada a geometrical approach abstract exploration within the slave craton has revealed clusters of kimberlite intrusions commonly with internally consistent geochemical and temporal characteristics translation diagrams fry analysis allow an unbiased geometrical examination of the distance and direction between each kimberlite occurrence and all others in the database recurrent patterns are visually accentuated due to the square function in data density circular histograms quantify the azimuthal density of kimberlite at various distances for this study the database comprises the geographic position of 212 kimberlite occurrences of which 70 are from the lac de gras field ldg analyses are presented separately for the ldg data and for all non ldg data in order to test for regional variations and to avoid overwhelming the craton scale studies by the high density of ldg data empirical grouping of kimberlite locations results in delineation of five elliptical clusters that encompass all but four kimberlite occurrences clusters within the western part of the craton are elongate to the north northeast and align within a narrow zone western corridor elsewhere the clusters are elongate to the northwest or west northwest and appear to be arranged en echelon within a poorly defined north northwest trending zone central corridor geometrical spatial analyses of kimberlite locations highlight the craton scale pattern of emplacement within the two main corridors at regional and local scales individual intrusions are preferentially located towards the west northwest ca 280 and north northeast ca 015 of other intrusions and these orientations are interpreted to reflect upper mantle trends in magma generation at local scales 10 25 km kimberlite of the central and southern craton tends to be located to the northeast ca 045 and possibly weakly to the east northeast ca 070 of other intrusions and these orientations correspond to major crustal fractures systems it is proposed that kimberlite emplacement is controlled primarily by the interaction of elongate 280 and 015 source regions with near surface deviations influenced by crustal fracture systems the 015 trend evident at craton regional and local scales is parallel to a swarm of alkaline diabase dykes that are concentrated in a ca 30 km wide corridor passing through lac de gras a profound spatial association between significantly diamondiferous kimberlite and the margins of the dyke corridor suggests the corridor is the surface expression of a mantle depth structure it remains unclear whether the proposed mantle structure coincides with a diamond rich zone near the base of the lithosphere or delineates pathways favorable for diamond preservation during emplacement the linear array of kimberlite within the western craton forms a parallel corridor that may be an analogous mantle structure but which to date has failed to yield economic diamond concentrations

spatial and temporal zoning of hydrothermal alteration and mineralization in the sossego iron oxide copper gold deposit carajas mineral province brazil paragenesis and stable isotope constraints the sossego iron oxide copper gold deposit 245 mt 1 1 cu 0 28 g t au in the carajas mineral province of brazil consists of two major groups of orebodies pista sequeirinho baiano and sossego curral with distinct alteration assemblages that are separated from each other by a major high angle fault the deposit is located along a regional wnw ese striking shear zone that defines the contact between metavolcano sedimentary units of the 2 76 ga itacaiunas supergroup and tonalitic to trondhjemitic gneisses and migmatites of the 2 8 ga xingu complex the deposit is hosted by granite granophyric granite gabbro and felsic metavolcanic rocks the pista sequeirinho baiano orebodies have undergone regional sodic albite hematite alteration and later sodic calcic actinolite rich alteration associated with the formation of massive magnetite apatite bodies both these alteration assemblages display ductile to ductile brittle fabrics they are cut by spatially restricted zones of potassic biotite and potassium feldspar alteration that grades outward to chlorite rich assemblages the sossego curral orebodies contain weakly developed early albitic alteration and very poorly developed subsequent calcic sodic alteration these orebodies contain well developed potassic alteration assemblages that were formed during brittle deformation that resulted in the formation of breccia bodies breccia matrix commonly displays coarse mineral infill suggestive of growth into open space sulfides in both groups of deposits were precipitated first with potassic alteration and more importantly with a later assemblage of calcite quartz epidote chlorite in the sequeirinho orebodies sulfides range from undeformed to deformed sulfides in the sossego curral orebodies are undeformed very late weakly mineralized hydrolytic alteration is present in the sossego currral orebodies the sulfide assemblage is dominated by chalcopyrite with subsidiary siegenite and millerite pyrrhotite and pyrite are minor constituents of ore in the sequerinho orebodies while pyrite is relatively abundant in the sossego curral bodies oxygen isotope partitioning between mineral pairs constrains temperatures in the deposit spatially and through time in the sequeirinho orebody the early sodic calcic alteration stage was characterized by temperatures exceeding 500 c and delta text 18 text o text h text 2 text o values for the alteration fluid of 6 9 0 9 temperature declines outward and upward from the zone of most intense alteration paragenetically later copper gold mineralization displays markedly lower temperatures 300 c and was characterized by the introduction of 18o depleted hydrothermal fluids 1 8 3 4 the calculated dh2o and delta text 18 text o text h text 2 text o values suggest that the fluids that formed the early calcic sodic alteration assemblage were of formational metamorphic or magmatic origin the decrease of delta text 18 text o text h text 2 text o values through time may reflect influx of surficially derived waters during later alteration and mineralization events influx of such fluids could be related to episodic fluid overpressure resulting in dilution and cooling of the metalliferous fluid causing deposition of metals transported as metal chloride complexes

what controls gold distribution in archean terranes despite intensive efforts determination of a predictable pattern of gold distribution to enhance process understanding and simplify exploration has remained elusive the pattern of gold distribution along the archean boulder lefroy shear zone in the yilgarn craton of western australia provides insights into gold distribution in one of the world s richest provinces four world class gold deposits including the giant golden mile at kalgoorlie are regularly spaced along the shear zone providing a window into understanding large scale archean hydrothermal systems relationships among gold endowment shear zone trend and geologic complexity as measured by fractal dimensions indicate that 1 ore fluids were focused into those parts of the shear zone with greatest misorientation from the regional trend which define dilational sites during shearing and became the sites of world class gold deposits and 2 the degree of complexity contrast along the shear zone modulated gold endowment

fractal analysis of fracture patterns using the standard box counting technique valid and invalid methodologies abstract on the basis of results of simple box counting analysis it has been suggested in several recent publications that natural fracture patterns are fractal fractal patterns are characterized by self similarity of structure on a range of scales and provide straight line distributions on box counting plots new analysis of a fracture pattern that provided the most convincing straight line box counting curve previously published shows that the curve is non linear and therefore that the fracture pattern is not fractal non linear box counting curves are also characteristic of other natural fracture patterns analysed but spurious linear curves can be obtained if the area analysed extends beyond the mapped area