mineralogical and isotopic record of biotic and abiotic diagenesis of the callovian oxfordian clayey formation of bure france abstract the callovian oxfordian cox clayey unit is being studied in the eastern part of the paris basin at depths between 400 and 500 m depth to assess of its suitability for nuclear waste disposal the present study combines new mineralogical and isotopic data to describe the sedimentary history of the cox unit petrologic study provided evidence of the following diagenetic mineral sequence 1 framboidal pyrite and micritic calcite 2 iron rich euhedral carbonates ankerite sideroplesite and glauconite 3 limpid calcite and dolomite and celestite infilling residual porosity in bioclasts and cracks 4 chalcedony 5 quartz calcite pyrite in bioturbations shows a wide range of 34s 38 to 34 5 providing evidence of bacterial sulphate reduction processes in changing sedimentation conditions the most negative values 38 to 22 measured in the lower part of the cox unit indicate precipitation of pyrite in a marine environment with a continuous sulphate supply the most positive pyrite 34s values 14 up to 34 5 in the upper part of the cox unit indicate pyrite precipitation in a closed system celestite 34s values reflect the last evolutionary stage of the system when bacterial activity ended however its deposition cannot be possible without sulphate supply due to carbonate bioclast dissolution the 87sr 86sr ratio of celestite 0 706872 0 707040 is consistent with deposition from jurassic marine derived waters carbon and oxygen isotopic compositions of bulk calcite and dolomite are consistent with marine carbonates siderite only present in the maximum clay zone has chemical composition and 18o consistent with a marine environment its 13c is however lower than those of marine carbonates suggesting a contribution of 13c depleted carbon from degradation of organic matter 18o values of diagenetic chalcedony range between 27 and 31 suggesting precipitation from marine derived pore waters late calcite crosscutting a vein filled with chalcedony and celestite and late euhedral quartz in a limestone from the top of the formation have lower 18o values 19 suggesting that they precipitated from meteoric fluids isotopically close to present day pore waters of the formation finally the study illustrates the transition from very active biotic diagenesis to abiotic diagenesis this transition appears to be driven by compaction of the sediment which inhibited movement of bacterial cells by reduction of porosity and pore sizes rather than a lack of inorganic carbon or sulphates

lithospheric structure beneath the south eastern zagros mountains iran recent slab break off integrated lithospheric modelling based on the combined interpretation of gravity geoid and topography data sets highlights a previously undocumented lithospheric thinning beneath the zagros collisional belt iran which we propose to relate to recent slab break off at the continent ocean transitional lithosphere recent published data on the distribution of seismicity at depth support this interpretation in agreement with other published models for the zagros mountains the overlying crust exhibits by contrast a noticeable thickening reaching a maximum of 52 km the consequent thermal uplift expected from slab break off is suggested to have modified the zagros wedge taper and triggered the recently documented switch from thin skinned to thick skinned deformation in the zagros fold thrust belt

aeromagnetic patterns of half graben and basin inversion implications for sediment hosted massive sulfide pb zn ag exploration the inverted extensional basins of the palaeoproterozoic north australian craton are amongst the most metallogenically endowed on earth for sediment hosted massive sulphide shms pb zn ag deposits faults that evolved during the evolution of these basins are an important exploration vector as they have behaved as conduits for mineralizing fluids controlled facies architecture and impacted on hydrothermal convection cells we attempt to map out ancient normal faults using integrated structural and aeromagnetic analysis to identify faults that are either buried beneath younger cover or have been inverted during later orogenic events this technique can be used for targeting potential conduits for mineralising fluids during shms pb zn ag exploration as well as a tool to map the architecture of extensional basins we have constructed simplified cross sections of half graben and inverted half graben and have forward modelled their magnetic response the aeromagnetic signature of a pre inverted half graben shows that the tilt block is characterised by a shallow magnetic gradient related to the shallowing of the magnetic marker beneath the half graben normal offset of the marker unit across a normal fault is characterised by a steeper magnetic gradient as the depth to the marker horizon increases simplified cross sections of isolated growth anticlines and the hanging wall buttressing show that the general shape of the magnetic profiles are maintained until the half graben has been completely inverted and the magnetic marker horizon displays reverse offset along the reactivated normal fault

metallogeny of the precambrian in iran abstract precambrian complexes are exposed in northern and central iran on the basis of the degree of metamorphism and lithology three major units can be distinguished the oldest complex consists of high grade metamorphosed and partly granitized gneisses followed by a low grade metamorphic series including amphibolites quartzitic schists and marbles these rocks are overlain by series of greenschist facies or slightly higher grade flyschoid rocks alkalic granites which have in places invaded the above series have produced skarn type magnetite fe ore and vein type au mineralization the third known complex consists of intracontinental rift type sediments evaporites pyroclastics and magmatic rocks the precambrian basement in iran is a part of the afro arabian platform consolidated by the kibaro pan african orogeny this tectonic event ended with tensional intracontinental rifting and the development of taphrogenic rift structures with bimodal alkaline and carbonatite type magmatism this magmatism and related alteration produced metasomatic rocks and associated mineralizations about 750 500 ma in age mineralizations of u th v mn mo ti ba apatite rare earth elements ree stratiform pb zn massive sulphides and different types of fe ore are found within these taphrogenic belts

location structure and seismicity of the seattle fault zone washington evidence from aeromagnetic anomalies geologic mapping and seismic reflection data a high resolution aeromagnetic survey of the puget lowland shows details of the seattle fault zone an active but largely concealed east trending zone of reverse faulting at the southern margin of the seattle basin three elongate east trending magnetic anomalies are associated with north dipping tertiary strata exposed in the hanging wall the magnetic anomalies indicate where these strata continue beneath glacial deposits the northernmost anomaly a narrow elongate magnetic high precisely correlates with magnetic miocene volcanic conglomerate the middle anomaly a broad magnetic low correlates with thick nonmagnetic eocene and oligocene marine and fluvial strata the southern anomaly a broad complex magnetic high correlates with eocene volcanic and sedimentary rocks this tripartite package of anomalies is especially clear over bainbridge island west of seattle and over the region east of lake washington although attenuated in the intervening region the pattern can be correlated with the mapped strike of beds following a northwest striking anticline beneath seattle the aeromagnetic and geologic data define three main strands of the seattle fault zone identified in marine seismic reflection profiles to be subparallel to mapped bedrock trends over a distance of 50 km the locus of faulting coincides with a diffuse zone of shallow crustal seismicity and the region of uplift produced by the m 7 seattle earthquake of a d 900 930

granite and gabbrodiorite associated skarn deposits of nw iran abstract field and laboratory studies show that there are two types of skarn deposits in nw iran granite associated type i and gabbrodiorite associated type ii granite associated deposits are accompanied by cu and fe mineralisation whereas mn and fe are the main ore metals in gabbrodiorite associated skarn deposits there are some differences in the mineralogy of these skarn deposits bixbyite piemontite and cr bearing garnet are found only in gabbrodiorite associated skarns whereas idocrase occurs only in granite associated deposits type ii skarns show exoskarn features whereas some type i skarns have developed endoskarn as well evidence of boiling of hydrothermal fluid can be seen in both types and seems to be a common mechanism of mineral deposition gabbrodiorite associated skarns show higher f o 2 than granite associated deposits based on mineralogical and textural evidence mineralisation in both groups has started from about 550 c early formed anhydrous minerals have begun to be replaced by hydrous minerals from about 400 c it seems that due to low fluid content in the gabbrodioritic magma heated meteoritic water in the surrounding volcanoclastic and tuffaceous rocks was the main source of hydrothermal solution in the gabbrodiorite associated skarn system

magnetostratigraphy of miocene pliocene zagros foreland deposits in the front of the push e kush arc lurestan province iran abstract the timing of the deformation in the zagros simply folded belt is poorly constrained because of the lack of an accurate absolute chronology of the syntectonic sedimentary sequences the foreland basin infill at the front of the push e kush arc is composed of fine grained fluvial plain deposits agha jari fm and coarse conglomerates at the top of the section bakhtyari fm a magnetostratigraphic study was carried out in a composite section spanning about 2800 m in order to date growth strata and to constrain the timing of the deformation in the mountain front flexure mff magnetostratigraphic correlation of the base of the agha jari fm with chron c5a yields an age of 12 8 to 12 3 ma for this base the transition to the conglomerates of the bakhtyari fm correlates with the upper gauss chron c2an at approximately 3 ma the deposition age of the top of the preserved bakhtyari fm is extrapolated around the pliocene pleistocene boundary the base of the agha jari fm growth strata and thus the beginning of the deformation in the front of the push e kush arc is dated at 8 1 7 2 ma the topmost preserved bakhtyari is folded in the ne flank of the changuleh anticline and is unconformably overlying the sw flank of the anaran anticline this indicates that the tectonic deformation in the front of the push e kush arc was active at least during 5 my the mff is a relatively long lived structure active from 8 1 to 7 2 ma to about the pliocene pleistocene boundary partly synchronous with the changuleh anticline to the foreland after mff tectonic cessation only the changuleh anticline remained active

the carbonate rock hosted epithermal gold deposit of agdarreh takab geothermal field nw iran hydrothermal alteration and mineralisation the disseminated gold deposit of agdarreh 24 5 t at 3 7 g t au is hosted in hydrothermally leached miocene reefal limestone in the takab geothermal field which is part of the cenozoic urumieh dokhtar volcanic arc of nw iran alteration and mineralisation are largely bedding controlled blanket like and include 1 pre ore decalcification 2 first stage silicification associated with pyrite early pyrite with 3 4 wt as late pyrite with 1 3 wt as and sphalerite 3 second stage silicification with precipitation of galena pb sb as sulphides sulphosalts tellurides and native bismuth 4 late stage cinnabar and barite in vugs 5 oxide ore stage and carbonate alteration complex mn fe rich oxyhydroxides arsenates sulphates aps minerals and rutile in residual leached rock and infill of karstic cavities gold occurs invisibly in the jasperoids and is enriched in the mn fe oxyhydroxide surface cap of the jasperoids gold mineralisation is associated with the hydrothermal metal suite of as sb hg te se tl ba zn ag cd bi and pb and is characterised by very low cu contents arsenian pyrite probably carried most of the primary invisible gold native gold occurs in association with the late stage cinnabar and the oxide ore

crustal lineament control on magmatism and mineralization in northwestern argentina geological geophysical and remote sensing evidence abstract the relationship between long lived deep crustal lineaments and the locations of magmatic centers and associated mineral deposits has been investigated in the puna region of northwestern argentina through the analysis of regional aeromagnetic surveys landsat images and geological information the good exposure and excellent preservation of basement and supracrustal geology in this region makes it particularly suitable for such a study at a regional scale several contrasting magnetic domains are recognized which correlate with crustal geology two basement domains are separated by a nne trending boundary which is believed to correlate with a paleozoic suture zone between the pampia to the southeast and arequipa antofalla terranes to the northwest locally overlying these basement terranes is the cenozoic magmatic domain which is best developed in the n s trending volcanic arc at the western edge of the puna the cordillera occidental in addition four southeast trending volcanic zones extend for several hundred kilometers across the puna many important mineral deposits and areas of hydrothermal alteration are associated with these volcanic breakouts and we have selected three such areas for more detailed study bajo de la alumbrera argentina s largest porphyry copper deposit cerro galan the largest ignimbrite caldera in argentina with associated hydrothermal alteration zones and el queva a historic polymetallic district located within a major volcanic range a comparison of lineament maps generated from aeromagnetic and landsat tm images reveals broad correlation between these different remote sensing techniques which respectively highlight subsurface magnetic and surface geological features in addition the locations of magmatic and hydrothermal centers can be related to the interpreted structural framework and are seen to occur near the intersections of major lineament zones it is suggested that in three dimensions such intersection zones form trans lithospheric columns of low strength and high permeability during transpressional or transtensional tectonic strain and may thereby serve as conduits for magma ascent to the shallow crust pooling of large volumes of deeply derived magma in shallow crustal magma chambers may then result in voluminous devolatilization and the formation of hydrothermal mineral deposits it is important to note that in this model structural intersections serve as facilitators for magma ascent and volatile exsolution but do not in themselves cause this process other factors such as magma supply rate and tectonic stress are essential primary ingredients and local magmatic and volcanic processes affect the ultimate potential for ore formation nevertheless we suggest that lineament analysis provides a valuable framework for guiding the early stages of mineral exploration other regional and local geological considerations must then be applied to identify priority targets within this framework

stable isotope s o h and c studies of the phyllic and potassic phyllic alteration zones of the porphyry copper deposit at sungun east azarbaidjan iran abstract the porphyry copper deposit pcd at sungun is located in east azarbaidjan nw of iran the magmatic suites in the sungun area are a part of the nw se trending cenozoic magmatic belt of iran the sungun porphyries occur as stocks and dikes the stocks are divided into two groups i and ii porphyry stock ii ranging in composition from quartz monzonite through granodiorite to granite hosts the sungun pcd four distinct types of hypogene alterations were recognized at sungun 1 potassic 2 potassic phyllic 3 phyllic and 4 propylitic stable isotope s o h and c studies were restricted to within the phyllic and potassic phyllic alteration zones where numerous cross cutting quartz sulfides carbonates and sulfate veinlets are present the objective of these studies was to determine the origin of the ore forming solutions and their important components e g sulfur and carbon twenty sulfide and four sulfate samples were taken from sulfide and gypsum veinlets within porphyry stock ii and the associated skarn zone for sulfur isotopic analyses the 34 s values of sulfides pyrite chalcopyrite molybdenite galena sphalerite and sulfate gypsum range from 4 6 to 0 2 mean of 1 5 and from 10 9 to 14 4 mean of 12 9 respectively these values are almost analogous to those from el salvador chile and ajo arizona and twin buttes arizona and strongly suggest a magmatic source for the sulfur at sungun twenty eight fluid inclusion rich quartz samples from quartz veinlets beneath the supergene zones of the porphyry stock ii were chosen for o and h isotopic analyses the 18 o of quartz and d of fluid inclusions in quartz values range from 8 3 to 10 2 mean of 9 2 and 58 to 75 mean of 66 relative to standard mean ocean water smow respectively the calculated 18 o values of the fluids range from 4 4 t 375 c to 7 6 t 570 c with a mean of 6 4 the 18 o and d values of the fluids lie within the typical range of magmatic waters based upon the lowest obtained d values the calculated maximum exchangeable meteoric water that might be involved in the phyllic and potassic phyllic alteration processes was 20 fourteen calcite samples from carbonate veinlets in the porphyry stock ii and two samples from associated marble aureole were collected for carbon and oxygen isotopic analyses the 13 c calcite from porphyry stock ii and associated marble aureole varies from 0 4 to 2 9 and 0 06 to 2 relative to the pdb standard of the university of chicago respectively the corresponding 18 o calcite values range from 6 to 13 2 relative to smow the 13 c values lie within the sedimentary range suggesting that there was little or almost no magmatic carbon in the hydrothermal system in contrast the 18 o calcite values are far lower than that of cretaceous sedimentary carbonates which suggest that the values were influenced by those of magmatic fluids through isotopic re equilibration these isotopic investigations demonstrated that 1 in contrast to some well known pcds about 80 of the fluids involved in the phyllic and potassic phyllic alterations at sungun had a magmatic o and h isotopic signature 2 the upper cretaceous limestone was the potential source of c and 3 the sulfur had a magmatic origin

evidence for a battle mountain eureka crustal fault zone north central nevada and its relation to neoproterozoic early paleozoic continental breakup 1 combined evidence from gravity radiogenic isotope and magnetotelluric mt data indicates a crustal fault zone that coincides with the northwest trending battle mountain eureka bme mineral trend in north central nevada usa the bme crustal fault zone likely originated during neoproterozoic early paleozoic rifting of the continent and had a large influence on subsequent tectonic events such as emplacement of allochthons and episodic deformation magmatism and mineralization throughout the phanerozoic mt models show the fault zone is about 10 km wide 130 km long and extends from 1 to 5 km below the surface to deep crustal levels isotope data and gravity models imply the fault zone separates crust of fundamentally different character geophysical evidence for such a long lived structure likely inherited from continental breakup defies conventional wisdom that structures this old have been destroyed by cenozoic extensional processes moreover the coincidence with the alignment of mineral deposits supports the assertion by many economic geologists that these alignments are indicators of buried regional structures

hypogene zn carbonate ores in the angouran deposit nw iran the world class angouran nonsulfide zn pb deposit is one of the major zn producers in iran with resources estimated at about 18 mt at 28 zn mainly in the form of the zn carbonate smithsonite this study aims to characterize these carbonate ores by means of their mineralogy and geochemistry which has also been extended to the host rocks of mineralization and other local carbonate rock types including the prominent travertines in the angouran district as well as to the local spring waters petrographical chemical and stable isotope o h c sr data indicate that the genesis of the zn carbonate ores at angouran is fairly distinct from that of other classical nonsulfide zn deposits that formed entirely by supergene processes mineralization occurred during two successive stages with the zinc being derived from a preexisting sulfide ore body a first main stage of zn carbonates stage i carbonate ore is associated with both preexisting and subordinate newly formed sulfides whereas a second stage is characterized by supergene carbonates zn and minor pb coexisting with oxides and hydroxides stage ii carbonate ore the coprecipitation of smithsonite with galena pyrite and arsenopyrite as well as the absence of fe and mn oxides hydroxides and of any discernible oxidation or dissolution of the sphalerite rich primary sulfide ore shows that the fluids responsible for the main stage i carbonate ores were relatively reduced and close to neutral to slightly basic ph with high fco2 smithsonite 18ovsmow values from stage i carbonate ore range from 18 3 to 23 6 while those of stage ii carbonate ore show a much smaller range between 24 3 and 24 9 the 13c values are fairly constant in smithsonite of stage i carbonate ore 3 2 6 0 but show a considerable spread towards lower 13cvpdb values 4 6 to 11 2 in stage ii carbonate ore this suggests a hypogene formation of stage i carbonate ore at angouran from low temperature hydrothermal fluids probably mobilized during the waning stages of tertiary quaternary volcanic activity in an environment characterized by abundant travertine systems throughout the whole region conversely stage ii carbonate ore is unambiguously related to supergene weathering as evidenced by the absence of sulfides the presence of fe mn oxides and arsenates and by high 18o values found in smithsonite ii the variable but still relatively heavy carbon isotope values of supergene smithsonite ii suggests only a very minor contribution by organic soil carbon as is generally the case in supergene nonsulfide deposits

origin and evolution of the seattle fault and seattle basin washington analysis of seismic reflection data reveals that the seattle basin washington is markedly asymmetric and consists of 9 10 km of eocene and younger deposits the basin began as a discrete geologic element in the late eocene 40 ma the result of a reorganization in regional fault geometry and kinematics in this reorganization dextral offset on the puget fault south east of seattle stepped eastward and the seattle fault began as a restraining transfer zone north vergent reverse or thrust faulting on the seattle fault forced flexural subsidence in the seattle basin to the north offset on the seattle fault and subsidence of the seattle basin have continued to the present

eocene gold ore formation at muteh sanandaj sirjan tectonic zone western iran a result of late stage extension and exhumation of metamorphic basement rocks within the zagros orogen a multidisciplinary study including field geology microstructure analysis 40ar 39ar dating and fluid inclusion microthermometry and raman spectrometry has been carried out on the muteh gold deposit located in a greenschist to amphibolite facies metamorphic rock complex of the sanandaj sirjan tectonic zone zagros orogen iran the muteh gold deposit has been previously interpreted as genetically related to precambrian granitic intrusions as an exhalative hot spring deposit related to paleozoic rhyolitic acidic tuffs and to local metamorphic processes host rocks of the gold deposit are predominantly schist and gneiss and subsidiary amphibolite and quartzite and are intruded by leucogranites in the vicinity of the gold deposit the metamorphic and granitic rocks display a subhorizontal mylonitic foliation containing a northeast oriented stretching lineation field investigations in one of the producing open pits show that the gold orebodies are controlled by northwest oriented normal faults and joints dipping to the northeast and the southwest and crosscutting the ductile fabric of the host rocks both the ductile fabric of the host rocks and the gold ore controlling brittle structures are interpreted to have formed within a single continuous extensional event which started with ductile deformation and gradually changed into brittle deformation hydrothermal alteration associated with ore formation consists of quartz muscovite pyrite dolomite ankerite and albite which crosscuts the ductile fabric and overprints the metamorphic minerals of the host rocks pyrite is the dominant opaque mineral and is the major phase associated with gold chalcopyrite marcasite bismuth galena sphalerite and pyrrhotite are subsidiary to rare phases 40ar 39ar incremental heating and in situ laser ablation age data reveal a coherent sequence of cooling and hydrothermal events in the metamorphic complex hosting the muteh gold deposit muscovite samples from the alteration zone and from one quartz vein from the orebodies yield 40ar 39ar ages between 55 7 and 38 5 ma and show that gold mineralization is the youngest among the different dated events this eocene age is consistent with the young structural setting of the gold orebodies revealing an emplacement along northwestoriented normal faults which can be correlated with tertiary extensional tectonic events reported by previous field investigations the data also indicate that gold ore formation is coeval with magmatism in the adjacent tertiary urumieh dokhtar magmatic belt and with intrusive activity within the sanandaj sirjan zone with a 40ar 39ar age of 54 ma near muteh according to our study the remaining 40ar 39ar data reveal a cretaceous to early tertiary metamorphic magmatic and deformation history of the complex hosting the muteh gold deposit the fluid inclusion study showed that distinct fluids were present during the regional geologic evolution predating ore formation and later eocene gold ore formation early regional fluids consist of an h2o co2 nacl fluid with subsidiary n2 and ch4 that underwent local unmixing the salinities of the liquid rich inclusions resulting from unmixing range between 2 2 and 17 5 wt percent nacl equiv and those of the co2 rich vaporrich inclusions range between 2 8 and 7 2 wt percent nacl equiv the high salinity of the regional liquid rich fluids is attributed to metamorphism of evaporite bearing sedimentary rocks magmatic intrusions retrograde hydration reactions metamorphism of impure marbles and migmatization the fluid inclusions spatially associated with the gold veins postdating regional metamorphism and ductile deformation of the host rocks contain a low salinity aqueous fluid with a dilute low density co2 component and maximum salinities between 2 6 and 5 8 wt percent nacl equiv gold deposition at muteh occurred during or after late stages of eocene brittle extension as a result of exhumation of the host metamorphic complex possibly during magmatic activity in the sanandaj sirjam zone it is most likely linked to the introduction of a distinct low salinity low co2 content aqueous fluid during crustal extension these fluids are younger than and therefore unrelated to the highly saline and co2 rich regional metamorphic magmatic fluids our results refute previous models advocating precambrian to paleozoic ages of the muteh gold deposit

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

distribution of orogenic gold deposits in relation to fault zones and gravity gradients targeting tools applied to the eastern goldfields yilgarn craton western australia a quantitative spatial analysis of mineral deposit distributions in relation to their proximity to a variety of structural elements is used to define parameters that can influence metal endowment deposit location and the resource potential of a region using orogenic gold deposits as an example geostatistical techniques are applied in a geographic information systems based regional scale analysis in the high data density yilgarn craton of western australia metal endowment gold production and gold rank per square kilometer is measured in incremental buffer regions created in relation to vector lines such as faults the greatest metal tonnages are related to intersections of major faults with regional anticlines and to fault jogs particularly those of dilatant geometry using fault length in parameter search there is a strong association between crustal scale shear zones faults and deposits nonetheless it is the small scale faults that are marginal or peripheral to the larger scale features that are more prospective gravity gradients depicted as multiscale edges or gravity worms show a clear association to faults that host gold deposits long wavelength long strikelength edges interpreted as dominantly fault related have greater metal endowment and provide a first order area selection filter for exploration particularly in areas of poor exposure statistical analysis of fault fold and gravity gradient patterns mainly affirms empirical exploration criteria for orogenic gold deposits such as associations with crustal scale faults anticlinal hinge zones dilational jogs elevated fault roughness strong rheological contrasts and medium metamorphic grade rocks the presence and concurrence of these parameters determine the metallogenic endowment of a given fault system and segments within the system by quantifying such parameters the search area for exploration can be significantly reduced by an order of magnitude while increasing the chance of discovery

copper mineralization around the ahar batholith north of ahar nw iran evidence for fluid evolution and the origin of the skarn ore deposit abstract this investigation presents and interprets fluid inclusion data from different lithological units of the cu skarn deposits at mazraeh north of ahar azarbaijan nw iran the results provide an assessment of the p t conditions and mineral fluid evolution and suggest new exploration parameters five types of inclusions are recognized from quartz and garnet the temperature of homogenization of type i inclusions with daughter minerals halite and sylvite ranges from 312 to 470 c with total salinity of 52 to 63 wt nacl equiv type ii and iii inclusions with halite have homogenization temperatures of 230 to 520 c and salinity of 31 to 50 wt nacl equiv the salinity of types iv and v biphase liquid vapor inclusions based on their final ice melting temperature varies between 10 2 to 20 8 wt nacl equiv t h vs salinity plots of inclusions show that the salinity of the fluids correlates positively with temperature the inclusions formed at low pressure changes in the temperature and salinity of the fluids can be reconstructed from the inclusions highly saline high temperature fluids were most abundant during the main chalcopyrite ore forming phase in the skarn and mineralized quartz veins low salinity aqueous fluids were abundant in barren veins in which there is no evidence for early hot high salinity brine and might have resulted from late stage dilution and mixing of hydrothermal fluids with meteoric water based on petrographic features and fluid inclusion data early stage magnetite deposition is related to boiling of fluid at temperatures of about 500 c at a later stage boiling at temperatures of around 320 to 400 c favored the deposition of sulfides and fe mobility was decreased at these lower temperatures the following inclusion characteristics may be used as exploration parameters in the mazraeh area i presence of high temperature salt bearing inclusions with t h between 300 and 500 c ii high salinity fluid inclusions and iii inclusions showing evidence of boiling of the fluid in addition the presence of magnetite is an important exploration parameter

1 subduction slab detachment and mineralization the neogene in the apuseni mountains and carpathians abstract the inner carpathians comprise several distinct neogene late stage orogenic pb zn cu ag au ore districts the mineral deposits in these districts are closely related to volcanic and subvolcanic rocks and represent mainly porphyry and epithermal vein deposits which formed within short periods of time in each district here we discuss possible geodynamic and structural controls that suggest why some of the neogene volcanic districts within the carpathians comprise abundant mineralization while others are barren the neogene period has been characterized by an overall geodynamic regime of subduction where primary roll back of the subducted slab and secondary phenomena like slab break off and the development of slab windows could have contributed to the evolution location and type of volcanic activity structural features developing in the overlying lithosphere and visible in the carpathian crust such as transtensional wrench corridors block rotation and relay structures due to extrusion tectonics have probably acted in focusing hydrothermal activity as a result of particular events in the geodynamic evolution and the development of specific structural features mineralization formed during fluid channelling within transtensional wrench settings and during periods of extension related to block rotation in the slovakian ore district of the western carpathians neogene volcanism and associated mineralization were localized by sinistral ne trending wrench corridors which formed part of the extruding alcapa block the baia mare ore district in the eastern carpathians reflects a transtensional wrench setting on distributed oversteps close to the termination of the dragos voda fault there mineralization was spatially controlled by the transtensional dragos voda master fault and associated cross fault systems the golden quadrangle cu au ore district of the southern apuseni mountains reflects an unusual rotated transtensional extensional setting close to the termination of a graben system there fluid flow was probably localized by fault propagation at the inner tip of the graben system the spatial and temporal evolution of the magmatism and its changing geochemical signature from n w to s e strongly suggests a link with the contemporaneous northeastward roll back of the subducted slab and a progressive southeastward detachment during accelerating roll back this geodynamic evolution is further supported by the present day overall and detailed mantle lithospheric density images the present day heat flow patterns the crustal architecture and its interpreted evolution and the spatial and temporal evolution of depocentres around the carpathian arc in contrast to all these features the mineral deposits in the west carpathians east carpathians and apuseni mountains are too synchronous with respect to their individual volcanic history and contrast too much with younger volcanics of similar style but barren in southeastern parts of the carpathians to simply link them directly to the slab evolution in all three districts the presence of magmatic fluids released from shallow plutons and their mixing with meteoric water were critical for mineralization requiring transtensional or extensional local regimes at the time of mineralization possibly following initial compressional regimes these three systems show that mineralization was probably controlled by the superposition of favourable mantle lithospheric conditions and partly independent evolving upper crustal deformation conditions in the 13 to 11 ma period the dominant mineralization formed all across the carpathians and was superimposed on structurally favourable crustal areas with at that time volcanic hydrothermal activity the period may reflect the moment when the upper part of the crust failed under lithospheric extension imposed by the slab evolution this crustal failure would have fragmented the overriding plate possibly breaking up the thermal lid to provoke intensive fluid flow in specific areas and allowed subsequent accelerated tectonic development block rotation and extrusion of a family of sub blocks that are arbitrarily regarded as the tisia dacia or alcapa blocks even though they have lost their internal entity

marble hosted sulfide ores in the angouran zn pb ag deposit nw iran interaction of sedimentary brines with a metamorphic core complex the angouran zn pb ag deposit zanjan province nw iran is located within the central sanandaj sirjan zone of the zagros orogenic belt the deposit has proven and estimated resources of 4 7 mt of sulfide ore at 27 7 zn 2 4 pb and 110 g t ag and 14 6 mt of oxidized carbonate ores at 22 zn and 4 6 pb it is hosted by a metamorphic core complex that is unconformably overlain by a neogene volcanic and evaporite bearing marine to continental sedimentary sequence the sulfide orebody precursor to the significant nonsulfide ores is located at the crest of an open anticline at the contact between neoproterozoic to cambrian footwall micaschists and hanging wall marbles 40ar 39ar data on muscovite from mineralized and unaltered footwall micaschists suggest a rapid mid miocene exhumation of the metamorphic basement 20 ma and yield an upper age constraint for mineralization the fine grained sulfide ore is massive replacive often brecciated clearly postmetamorphic and dominated by fe poor sphalerite with minor galena pyrite anhydrite quartz muscovite dolomite and rare calcite sphalerite contains na ca cl brine inclusions 23 25 mass total dissolved solids with homogenization temperatures of 180 70 c fluid inclusion chemistry na k li ca mg cl br ore geochemistry s and pb isotope data suggest that the angouran sulfide ore formed by the interaction of modified strongly evaporated miocene seawater and the lithotypes of an exhumed metamorphic core complex minor contributions of metals from miocene igneous rocks cannot be excluded mineralization occurred in a collisional intra arc setting with high heat flow probably during the transition from an extensional to a compressional regime the angouran deposit may represent a new type of low temperature carbonate hosted zn pb ore that is distinct from mississippi valley type and sedimentary exhalative deposits

structures of the zagros fold thrust belt in iran the zagros fold thrust belt in iran forms the external part of the zagros active orogenic wedge it includes a sequence of heterogeneous latest neoproterozoic phanerozoic sedimentary cover strata 7 to 12 km thick and composed of alternating incompetent and competent layers overlying precambrian crystalline basement with a complex pre zagros structural fabric balancing structures of the cover statigraphic units in the zagros fold thrust belt requires in sequence and out of sequence involvement of the precambrian basement in the deformation six detailed balanced and retrodeformable cross sections which are constructed based on geological and geophysical data across various sectors of the belt show fault bend and fault propagation folds interpreted to have formed by slip on their subjacent thrusts out of sequence basement rooted thrusts as the interpretations in the constructed cross sections suggest have breached the cover basement interface and using incompetent cover strata for propagation cut across the cover structures and have created associated new folds superimposed upon the pre existing structures this style of deformation which has resulted in structural complexity of the belt characterizes a 200 to 300 km wide zone of distributed partly synchronous deformation with along strike and across strike variations it also implies that the zagros fold thrust belt as the external part of the orogenic wedge is still in its subcritical condition with internal deformation to achieve a critical taper in creating structural complexity in addition to out of sequence thrusting mechanically weak layers evaporites and mudstones of the cover strata have played a significant role by providing several detachment horizons shortening estimates across the belt are variable based on the constructed cross sections and their restorations minimum shortening estimates range from 16 percent to 30 percent in different sectors of the belt

lead isotope signatures of the igneous rocks and porphyry copper deposits from the kerman cenozoic magmatic arc se iran and their magmatic metallogenetic implications abstract copper deposits in the kerman cenozoic magmatic arc kcma of iran are genetically related to miocene porphyries the porphyries and their associated cu deposits were intruded and emplaced into eocene volcanic sedimentary successions lead isotope compositions of the eocene volcanic rocks exhibit homogeneous non radiogenic values 206 pb 204 pb 18 40 to 18 49 207 pb 204 pb 15 41 to 15 48 and 208 pb 204 pb 38 15 to 38 36 in contrast the miocene ore hosting porphyries and associated sulfide minerals also show a relatively radiogenic and homogenous pb isotopic values with orogen character 206 pb 204 pb 18 52 to18 60 207 pb 204 pb 15 58 to 15 64 and 208 pb 204 pb 38 57 to 38 80 the shift in the pb isotopic composition of igneous rocks with time towards higher pb isotopic values precludes derivation of the ore hosting porphyries from a reservoir of similar composition to those in the eocene volcanic rocks the non radiogenic pb isotope signature of the eocene volcanic rocks indicates an origin from subduction related mantle derived magmas whereas the higher pb isotopic values of the miocene ore hosting porphyries suggest an increasing involvement of crustal materials with lower u pb ratios than the upper crust in the source region of these rocks combining the pb isotope data with petrogenetic considerations suggests derivation of the middle miocene ore hosting porphyries from a mixed reservoir with slightly radiogenic pb values such as a hybridized lower continental crustal source this source probably formed because of the involvement of cretaceous oligocene subduction related mantle derived mafic magmas at the base of arc crust the contribution of the miocene collision related mantle derived mafic magma in melting of the hybridized lower continental crust caused generation of the middle miocene porphyries hosting large copper deposits with the least 206 pb 204 pb ratios among other porphyries the higher 206 pb 204 pb ratios of the late miocene pliocene porphyries hosting small copper deposits as well as barren porphyries may reflect a decreasing involvement of collision related mantle derived mafic magma in the source of the late miocene pliocene porphyries the overall similarity in pb isotope values between sulfide minerals and ore hosting porphyries suggests a magmatic source for most of the pb and possibly other metals the more radiogenic isotopic ratios of some late sulfide minerals suggest an insignificant metal contribution from an external source such as local country rocks during hydrothermal circulation

tectonic evolution of the orogenic belt in the region located between kerman and neyriz abstract tectonic evolution of the orogenic belt in the region located between kerman and neyriz is explored within the context of two ne dipping neotethyan subduction zones the northern subduction zone was responsible for formation of the mesozoic sanandaj sirjan magmatic arc and the late cretaceous shahr babak baft ensimatic back arc extensional basin the southern subduction zone was responsible for formation of the reverse primitive neyriz island arc the central iranian volcanic belt and its line of porphyry copper deposits as well as the rafsanjan back arc extensional basin proto rafsanjan depression due to the collision of the neyriz island arc with the sanandaj sirjan active continental margin the shahr babak baft back arc basin was tectonically inverted into the shahr babak baft ophiolite belt finally the continental collision between the arabian and the central iranian plates took place during the neogene this led to the tectonic inversion of the rafsanjan ensialic basin into the rafsanjan retro arc basin the present rafsanjan depression and emplacement of the syncollision to late or post orogenic granitoid rocks felsic mass in the rafsanjan region

recognition of the regional lineaments of iran using geospatial data and their implications for exploration of metallic ore deposits abstract the relationship between major structural lineaments and locations of ore deposits in iran has been investigated using geospatial data in the course of lineament extraction satellite images aeromagnetic data digital elevation model dem and structural maps were processed and the lineaments and large scale faults were identified the extracted lineaments based on subjective assessment from each dataset were imported into gis software and the lineament map of iran was prepared by data integration the analysis for selecting significant lineament was mainly based on fault correlated lineament and lineament with field map fractures which was sets as benchmarks for compiling a final output map four major regional lineament trends of n s e w nw se and ne sw were identified in the data of all images which are corresponded to the structural zones and the major fault systems of iran the mineral deposits active and abandoned and mineral indications database compiled are based on the published maps papers reports and the ore deposits data files of geological survey of iran integrating the output of these two datasets by gis software resulted in the combined map of lineaments and gold copper lead zinc and iron deposits of iran the number and distance of ore deposits toward the lineaments were processed by the counting and cumulative methods in the gis software s approximately over 90 of the ore deposits of iran are located in the central part of the lineaments 15 km on each side which are concordant with a definition of large lineament about 50 of these mineral deposits are closer than 5 km to the lineaments there are significant correlations between lineament density and intersections with ore deposits occurrences the observed associations at this scale are informative in establishing exploration strategy and decreasing exploration risks for detailed work on ore deposit scale

fluid inclusion and stable isotope study of the esfordi apatite magnetite deposit central iran a reply sir we are pleased that our recent paper in economic geology jami et al 2007 presenting the geologic setting a description of the mineralization fluid inclusion and o isotope analyses of the esfordi p fe oxide deposit in central iran has been of interest to aftabi and his colleagues aftabi et al 2009 the opportunity to discuss further some aspects of our paper is appreciated including support for a hydrothermal dominated depositional model for esfordi aftabi et al 2009 focus their comments on the question of the affinity of the esfordi p fe oxide deposit in particular they argue that esfordi and by inference other diverse fe oxide deposits within the bafq district of central iran should be considered rapitan type banded iron formations i e bif klein 2005 rather than kiruna type hitzman 2000 in discussing our results and conclusions in the light of previous work particularly forster and jafarzadeh 1994 aftabi et al 2009 have misconstrued our interpretation of some of the textural and isotopic data as providing support for an orthomagmatic model for the esfordi p fe oxide deposit based on the structure relationships between mineralization and host rocks fluid inclusion and isotopic data we concluded that esfordi exhibits strong evidence of hydrothermal origin though we did not preclude some component of precursor orthomagmatic processes in formation of the p fe mineralisation it is noted that some examples of the kiruna end member of the continuum of fe oxide deposits discussed by hitzman 2000 are controversial particularly in regard to their evolution sillitoe and burrows 2002 henriquez et al 2003 we have shown that esfordi has a number of features typical of the kiruna type deposits and does not exhibit features consistent with an affinity to rapitan type fe oxide deposits this evidence will be discussed briefly with further data

the kuh e surmeh mineralization a carbonate hosted zn pb deposit in the simply folded belt of the zagros mountains sw iran the kuh e surmeh carbonate hosted zinc lead deposit located within the simply folded belt of the zagros mountains in southwestern iran is an orogen related mississippi valley type deposit originally formed in the foreland thrust belt of the zagros mountains structural and textural observations indicate that ore deposition took place as open space fillings in brecciated carbonate rock and as internal sediments consisting of fine grained ore minerals interlayered with carbonates the preferred genetic model for the concentration of the ore metals is that of dewatering of the zard kuh basin due to regional tectonic compaction tectonism and expulsion of basin derived fluids into the highly porous and brecciated dolomitized rocks of the dalan formation the metals precipitated from dense basinal brine 15 wt equiv nacl at low temperatures less than 200 c typically within strata of a late paleozoic carbonate platform

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

cu ni co as u mineralization in the anarak area of central iran abstract cu ni co as u mineralization in the anarak area of central iran occurs at the intersection of the uroumieh dokhtar magmatic belt with the great kavir doruneh fault in the area the volcanism associated with the magmatic belt is shoshonitic in character chemical analyses indicate that these are subduction related magmas detailed investigations in the vicinity of the talmessi mine indicate that mineralization occurred in two separate stages a first stage of copper sulphide mineralization with a relatively simple mineralogy and associated with the eocene magmatism and a second stage of cu ni co as u mineralization with a complex mineralogy which probably formed during another phase of deformation in the upper miocene this later deformation reactivated previously formed faults the mineralogy element association and isotopic composition of carbonates for the second phase of mineralization suggest a different origin to that of the first phase the fluids are likely to be non magmatic in origin possibly showing an increased input from meteoric waters the close spatial association with basic ultrabasic igneous rocks indicates that these may be the source through alteration and remobilization the arsenide mineralization in the anarak area shows many features that are similar to those of the classic five element deposits

recycling of orogenic arc crust triggers porphyry cu mineralization in kerman cenozoic arc rocks southeastern iran pre collisional eocene oligocene arc diorites quartzdiorites granodiorites and volcanic equivalents in the kerman arc segment in central iran lack porphyry cu mineralization and ore deposits whereas collisional middle late miocene adakite like porphyritic granodiorites without volcanic equivalents host some of the world s largest cu ore deposits petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment ore hosting kuh panj porphyry intrusions exhibit high sr 400 ppm low y 20 no negative eu anomalies eu eu 1 and relatively non radiogenic sr isotope signatures 87sr 86sr 0 7042 0 7047 relative to eocene oligocene granitoids mainly sr 12 la yb 15 eu eu 1 87sr 86sr 0 7053 0 7068 trace element modeling indicates peridotite melting for the barren eocene oligocene intrusions and a hydrous garnet bearing amphibolite source for middle late miocene ore hosting intrusions the presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30 35 to 40 45 km or 12 kbar the changes in residual mineralogy in the source of eocene to miocene rocks in the kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel underplating of cu and sulfur rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust mantle boundary and dehydration melting under oxidizing conditions produced syn and post collisional ore hosting intrusions while the lack of post collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur rich and oxidized adakitic magmas

the structure and kinematics of the southeastern zagros fold thrust belt iran from thin skinned to thick skinned tectonics 1 we present the first complete balanced cross section across the southeastern zagros fold thrust belt zftb the following main structural features emerge from this section 1 in the south of the zftb the proterozoic to recent sedimentary sequence has been decoupled from its panafrican basement along the ductile basal evaporites and folded into a series of large detachment anticlines ongoing shortening of these structures has resulted in migration of the basal salt layers into the cores of the anticlines and propagation of forelimb thrusts 2 in the north of the zftb deep seated ramps have folded the hanging wall rocks and produced imbrications and duplex structures within the higher levels of the sedimentary sequence 3 out of sequence thrusts linked to major seismogenic basement faults have cut through the structures in the cover of the zftb a three step incremental restoration of the section shows that two main phases of deformation can be separated in the tectonic evolution of the zftb a mio pliocene thin skinned phase in the course of which most of the structures in the cover were generated followed by a pliocene to recent thick skinned phase expressed as out of sequence faulting in the cover which is currently underlined by the seismicity within the basement in plan view the initial structures of the southeastern zftb developed with a curved shape essentially controlled by the shape and thickness of the underlying proterozoic salt basin i e the jura style in the following basement involved phase out of sequence thrusts cut at oblique angles through the preexisting structures of the cover the total shortening absorbed in the cover amounts to at least 45 km corresponding to a ratio of 22

cretaceous tertiary convergence and continental collision sanandaj sirjan zone western iran abstract the sanandaj sirjan zone contains the metamorphic core of the zagros continental collision zone in western iran the zone has been subdivided into the following from southwest to northeast an outer belt of imbricate thrust slices radiolarite bisotun ophiolite and marginal sub zones which consist of mesozoic deep marine sediments shallow marine carbonates oceanic crust and volcanic arc respectively and an inner complexly deformed sub zone late palaeozoic mesozoic passive margin succession rifting and sea floor spreading of tethys occurred in the permian to triassic but in the sanandaj sirjan zone extension related successions are mainly of late triassic age subduction of tethyan sea floor in the late jurassic to cretaceous produced deformation metamorphism and unconformities in the marginal and complexly deformed sub zones deformation climaxed in the late cretaceous when a major southwest vergent fold belt formed associated with greenschist facies metamorphism and post dated by abundant palaeogene granitic plutons in the southwest of the zone a late cretaceous island arc passive margin collision occurred with ophiolite emplacement onto the northern arabian margin similar to that in oman final closure of tethys was not completed until the miocene when central iran collided with the northeast arabian margin

emarat carbonate hosted zn pb deposit markazi province iran a geological mineralogical and isotopic s pb study abstract the emarat deposit with a total proved reserve of 10 mt ore grading 6 zn and 2 26 pb is one of the largest zn pb deposits in the malayer esfahan belt the mineralization is stratabound and restricted to early cretaceous limestones and dolomites the ore consists mainly of sphalerite and galena with small amounts of pyrite chalcopyrite calcite quartz and dolomite textural evidence shows that the ore has replaced the host rocks and thus is epigenetic sulfur isotopes indicate that the sulfur in sphalerite and galena has been derived from cretaceous seawater through thermochemical sulfate reduction sulfur isotope compositions of four apparently coprecipitated sphalerite galena pairs suggest their precipitation was under equilibrium conditions the sulfur isotopic fractionation observed for the sphalerite galena pairs corresponds to formation temperatures between 77 c and 168 c which agree with homogenization temperatures of fluid inclusions lead isotope studies indicate that the lead in galena has been derived from heterogeneous sources including orogenic and crustal reservoirs with high 238 u 204 pb and 232 th 204 pb ratios ages derived from the pb isotope model give meaningless ages ranging from early carboniferous to future it is probable that the pb isotope model ages that point to an earlier origin than the early cretaceous host rocks are derived from older reservoirs in the underlying carboniferous or jurassic units either from the host rocks or from earlier formed ore deposits within these units this research and other available data show that the emarat zn pb deposit has many important features of mississippi valley type mvt lead zinc deposits and thus we argue that it is an mvt type ore deposit

whitings a sedimentologic dilemma whitings drifting clouds of water milky because of suspended carbonate have been claimed to originate from either the action of bottom feeding fish or direct precipitation of calcium carbonate five cruises during different seasons were made to the great bahama bank to collect data pertinent to the controversy measurements of particulate concentrations average 10 mg liter with a maximum of 20 mg liter of carbonate sediment suspended in whiting water compared with an average of 1 5 mg liter for clear water outside the whitings the particles are dominantly acicular aragonite but mg calcite composes as much as 20 percent of some whitings sedimentation rates measured with fixed and drifting sediment traps were as great as 34 g m 2 hr sediment suspended in whitings aggregated into silt and sand size fioccules and settled to the bottom of settling tanks within six hours even on a rocking ship sediment in artificial whitings created by stirring sediment from the bottom with a shrimp trawl settled to the bottom in about the same time natural whitings on the other hand were never observed to dissipate because sedimentation from whitings occurs at rates sufficient to cause dissipation of the whitings within six hours we conclude that the natural whitings are continually replenished by direct precipitation the search for fish in whitings utilized sidescan sonar and fathometer imaging shrimp trawls rotenone remote video and direct scuba observation these methods and 25 years of casual observations leading to this study indicate that fish are not involved in the formation of most bahamian whitings several whitings were found over rocky or sandy bottoms where there was no mud available for fish to suspend the distance of these whitings from areas of muddy bottom precluded their having been made elsewhere by fish stable carbon and oxygen isotopic analyses and delta 14 c activity are interpreted to indicate that the suspended sediment in whitings contains some precipitated calcium carbonate and is not merely bottom sediment stirred into suspension estimates indicate that the amount of new carbonate produced in whitings on the great bahama bank is substantially higher than that arising from algal production consequently the amount of sediment transported to deep water may be much greater than previously thought