DEPARTMENT OF THE INTERIOR 

FRANKLIN K. LANE, Secretary 

UNITED STATES GEOLOGICAL SURVEY 

GEORGE OTIS SMITH, Director 

PROFESSIONAL PAPER 120-E 

TWO LAMPROPHYRE DIKES NEAR SANTAQUIN 

AND MOUNT NEBO, UTAH 

BY • 

G. F. LOUGHLIN 

Publlsb,ed June 14, 1918 , 

Shorter contributions to general geology, 1918 

(Pa~res 101-109) 

WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1918 
PEPARTMENT OF THE INTERIOR . . 

FRANKLIN K .. LANE, Secretary 

UNITED STATES GEOLOGICAL SURVEY 

GEORGE OTIS SMITH, Director 

Professional Paper 120-E. 

TWO LAMPROPI-IYRE DIICES NEAR SANTAQUIN 

AND MOUNT NEBO, urrAH 

BY 

G. F. LOUGHLIN 

- . Published June 14, 1918 

Shorter contributi9ns to general geology, 1918. 

(Pages 101-109) 

WASHINGTON 

GOVERNl\fENT PRINTING OFFICE 

1918 
CONTENTS. 

Introduction .... _. ................... ~ .................... : ..... -.- ................................... ·- .. -

Local geology ............... -.-: ........... , ........ -·- ........... -.. ----·- ........ : ............. -.... -- .... -- · Stratigraphy .... _ ......... -.- ...... _ .. __ ._ ... __ .. ___ .... __ ... __ ,_ .. ____ .. _____ . ______________ :_. ____ .. 

Dike rocks ........ _ . _ .... _ .... __ . _ .. __ ..... _ .... __ .... __ .......... _ ........ : ...... _ . _ ... _ . _ .. _ ...... . 

Structure ...................... · ...... _ ..... _ ..... _· ................ _ ..... _._ ..... _ .................... . 

The dikes .............. :: . ............. : ....................................... · ..................... · ...... . 

~:;r:~o:;~ c!::a~t:;~ _· _· _· ~ ~ ~ ~ __ ._. _· _: ~ : ~ ~ ~ ~- ~ ~ ~ ._ ._ ~ ~ ~ ~ ._ ~ ~ ._ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ : ~ ~ ~ ~ ~ ~ __ ~ ~ ~ ~ ~ ~ : ~ ~ : ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ : ~ Northern dike .... · ....... , .......... -.-·- ...... _ ........ _ ... _._ .... _, ... _ ........... __ ............. . 

Southern dike ........ _ ........ _ . __ . _ .. __ ... _ . _ .... __ ......... · __ ...... _ ............ ___ ......... _ .. . 

Chemical coin position ................. _ ...... _.· ....................... ·.: .............................. . 

Classification ................... -·~ ... _._ ... _._ .... __ ._ ........ -... __ .. : ..... _ ........................ . 

Similar analyses of other rocks ..................................... __ .· ....... __ ........ _ .... _ ....... _ ..... .'. 

Correlation and genes~s ..... · ..................... ·.· ........... ~ ................. , ................ : . .......• 

ILLUSTRATION. 

Page. 

101 

101 

101 

101 

103 

103 

103 

103 

103 

104 

104 

.107' 

107 

108 

Page. 

FIGURE 13. Geologic map of the Santaquin and Mount Nebo region, Utah.................................... 102 

ll 

• 

* 
•• 

., .. 

TWO LAMPROPHYRE DIKES NEAR SANTAQUIN AN.D MOUN~ NEBO, UTAH. 

By G. F. LouGHLIN. 

INTRODUCTION. of Cambrian age and the higher beds certainly 

No description of lamprophyre dikes in Utah ··of Mississippian age .. The upper Mississippian 

has heretofore been published/ and this paper includes thin quartzite beds intercalated with 

is presented as an addition to the petrology of limestone arid shale. The limestones form the 

the State. The two dikes here described are g~eater part of the range throughout the regio~, on the west slope of the Wasatch Mountains, occupying most of the summit areas a~d upper 

near Santaquin and Mount Nebo, and were western slopes and extending down· to the west 

noted by the writer in 1912, while he was en,.. bas~ of 'the ninge in the Mount Nebo mining 

gaged in a reconnaissance of the ore deposits of district northeast of Mona. 

central Utah. · The Tertiary rocks. include coarse reddish 

'LOCAL GEOLOGY. 

STRATIGRAPHY. 

The steep western f1~ont of the Wasatch 

Mountains. in the Santaquin ai1d Mount N ebo 

region exp·oses rocks of pre-Cambrian,· Paleozoic, and Tertiary age, whose relations are 

complicated by overthrust and block faulting. 2 

·(See fig. 13.) · 

. The pre-Cambrian is represented by reddish 

gneissoid granite with pegmatite veins and 

included bodies of schist, exposed for 2 miles or 

m.ore along the lower west slope of the m~in 

range southeast of Santaq~. This granite is 

overlain unconformably by Cambrian quartzite, 

dipping 28° E., which .does not appear to be 

over 80.0 feet thick (aneroid measurement). 

The quartzite is. prominent along the middle 

west slope east of Santaquin. and about 5 miles 

northeast of Mona. It passes upward into 

Cambrian shale, whi<?h corresponds- to the 

Ophir formation to ·the north and west, and· 

this is followed by a great thickness of lime-· 

stones, the lower beds of which are probably 

I B.s. Butler has informed tho writer that he has noted several biotite 

· lamprophyre dikes during his recent detailed studies of the Cpttonwood 

and Park City area in Utah. 

• 2 .l.oughlin, G. F., Reconnaissance in tho southern Wasatch Monn· 

. tains, Utah.: Jour. Geology, vol. 21, pp. 447-451, 1913. · 

/$'· 

coi;lglomerate and concretionary limestone, 

whi~h rest unconformably upon the Mississippian. They veneer the low ridges south and 

southwest of Santaquin and are.very extensive 

on the east slope of the main range. These 

rocks are overlain by ·a: coarse latite or andesite breccia, rriost of whose outcrops have been 

reduced to aggregates of loose cobbles. 

DIKE ROCKS. 

rhe only intrusive rocks noted in tlie region. 

are the two lamprophyre dikes that form the 

subject of this paper. The northern dike is 

east of Santaquin, on the Black Balsam claim. 

It cuts pre-Cambrian granite, is .3 feet thick, 

trends northeastward1 and' dips about 70° SE. 

It is closely paralleledJor part of its course by 

a vein of calcite and fluorite which contains a 

little chalcopyrite, · g~ena, and corresponding 

oxidation minerals. The southern dike is south 

of the mouth of Bear Canyon, northeast of 

Mona, on the property· worked by the Eureka 

Leasing & Mining Co. in 1912. It cuts Mississippian limestone, is 4 feet wide, strikes N. 

45°-~0° E., and has a vertical dip. 

There is no local evidence by which these 

.dikes can be correlated with other igneous· 

rocks. · From their petrographic character, 

however, and their lack of deformation, it is 

101 
102 SHORTER CONTRIBUTIONS T'O GENERAL GEOLOGY, 1918. 

assumed that they represent a late stage of the I by gran<?diorite and quartz ·diorite to the 

Tertiary volcanic period, which is well repre- north 'in the Cot~onwood-American Fork resented by latites or andesites on -Long Ridge, gion.2 Lamprophyre dikes in the last-named 

s"E:::=:::3::::::::::::E=::::::::=r:==:=:J====o:i'::::==============:::::===::Js M 1 LES 

Contour interva1500 feet 

.IJatum is mean sea level 

·FIGURE 13.-Geologic map of the Santaquin and Mount Nebo region, Utah. JR, pre-Cambrian granite;£, Cambrian quartzite; Cm, Mississippi::m and earlier limestones; T, Tertiary conglomerate and volcanic rocks; L, lamprophyre dikes. List of mines: 1, Union Chief; 2, Santaquin 

C~ief_and Santaquin King; 3, Big Nebo; 4, Eva and Nebo Highlancl; 5, Spider; 6, Freddie Lode (Eureka Leasing Co.). 

west of Mona; by rhyolites, latites, and mon- region, according to Butler~ are the latest 'of the 

zonite farther west; in the Tintic district/ and intrusive rocks. " 

1 Lindgren, 'Valdemar, and Loughlin, G. F., Geology and ore deposits 

of the Tintic mining district, Utah: U.S. Geol. $1,lfvey Prof. Paper 107, 

pp. 42-75 (in press). 

2 Butler, B.S., and Loughlin, G. F., A reconnaissance of tho Cotto!J·-

wood-American Fork mining region, Utah: U. S. ·a col. Surve'y Bull. 620, 

pp. 174-177, 1916. 
•• 

LAMPROPHYRE DIK,ES ~EAR SANTAQUIN AND MOUNT NEBO, UTAH; 103 

STRUCTURE. 

The attitude of the strata is for the most. 

part homoclinal, with a prevaili11g dip of about 

30° E., but some folds with steep· to vertical 

dips ~re prominent cast and northeast of }.1ona. 

The most striking structural featur(3s of the 

region have been produced by overthrust and 

block faulting. The overthrusts are exposed,. 

megascopic . mineral, . forming irregular scales 

and tablets 3 millimeters or less i:n diameter .. 

These phenocrysts consEtute about 20 per cent 

of the rock and give it the characteristic lusterof lamprophyre. Alteration products of olivine, consisting largely of calcite in small 

thinly. scattered spots,_ are. visible. on close inspec~ion of tho dike near Santaquin. The application of dilute hydrochloric acid produces 

brisk effervescence ill both rocks. · . though not very clearly, east and south of 

Santaquin, near. the north and south ends of 

the pre-C111nbria11 granite area; also along the 

west base of the rarige about 5 miles northeast MICROSCOPIC CHARACTER. 

of :Mona. At all these places }.1ississippian NORTHERN DIKE. 

liinestone is overridden by Ca~brian quartzite. . . The overthrust northeast of Mona clea:rly ante-. T~e northern dike, as seen in thin section, 

dates the block faulting, as shown in figure 13. consists of a prevailingly glassy groundn1ass 

The relation of the overthrusts to local foiding crowded with· phenocrysts of augite; biotite, 

is not clear. They may be synchronous with olivine, and magnetite and minute crystals of 

or later than the· folding, which elsewhere .in apatite. Phenocrysts 0.5 to 1 rriillilheter in 

Utah is assigned to post-Jurassic time but diameter. consti.tute about ~5 per cent of the 

clearly antedates the intrusions of monzonite rock. Feldspar is present only in the ground-

~d related rocks with which ore deposits are mass. The feldspar and glass forn1 less than 

genetically connected. The- writer's .investi- 50 per cent of the rock. Calcite, fibrous inonogations in the Cottonwood-Ainerican ·Fork 1 and clinic amphibole, and chalcedonic quartz are 

West Tintic 2 districts, however, have proved alteration products. 

that .the overthrusts in those districts are older Augite is the most abundant microscopic 

than the ig~~eous. intrusions and a1~y accom- phenocryst, making up about .35 per cent of 

panying deformations, which are probably of the rock. It forms typically twinned prisearly Tertiary age, and he provisionally corre-· nlatic automorphic grains. The main part has 

lates the overthrusts in the· Santaquin ·and an extinction angle (r /'. {;) between 45° and 

Mount Nebo region·with those in the districts 50°, whereas that of a narrow l;llarginal zoneis 

mentioned. about 5o grea.ter. These angles do not accord 

The' block f~ulting is marked by ·norma) with Rosenbusch's statement 3 that the pyfaults of northward and east-I1ortheastward roxene's of lamprophyres are of the diopsidjc 

trends, most of which coincide in positio~1 with variety, and this. is one characteristic in which 

canyons. T~ese faults were formed by the the two dikes· are exceptional. The- augite is 

disturbances that .caused the main uplift. of the very free from alteration. 

W ~satch Mountains and the ranges of the Olivine in hypautomorphic crystals as much 

Great Basin. They are latertlian the volcanic as 2 millimeters long oi·iginally formed about 

breccia and. presumably later than the two 3· per cent of the. rock. These crystals are now 

lamprophy~·e dikes ·and the ore deposits of the mostly altered to aggregates of calcite and a 

region, but there is no means of comparinO' the finely fibrous to platy monoclinic amphibole. 

ago of the dikes with any local faulting. b A few crystals are replaced by· serpentine and 

calcite. No secondary magnetite .accompanies 

·THE DIKES. the alteration products. 

MEGASCOPIC CHARACTER. Biotite forms many irregular to automorphic 

Tho rocks are dark gray to black, den~e, and b;rown grains and tablets, most of them less 

porphyritic. · Biotite is the only conspicuous than 0.5 nlillimeter long but some more than 

1 Loughlin, G. F., op. cit., pp. 440-443. Butler, B.S., and Loughlin, 

0 .. F., A reconnaissance of the Cottonwood-Amerioon F~rk minin" 

n'gion, Utah: U.S. Geol. Smvey B~ll. 620, pp. 178-179, 191~. · "' 

2Butler, B. S., and Loughlin, G. F., Oro depo:!its of Utah: U. S. 

Geol. Survey Prof. Paper 111 (in press). 

1 millimeter. The larger· phenocrysts have 

borders that are darket: brown than !Jhe main 

part, a common feature in the biotite of lampro3 Rosenbusch, H., Elemente der Gesteinslehre,·p. 233,-1906. 
104 SHORTER CONTR.IBUTIONS TO GENERAL GEOLOG~, 1918. 

phyres. All the biotite is of distinctly later 

growth than augite and olivine. As a whole it 

is free from alteration, but .a few of the htrger 

phenocrysts contain _a little calcl.te. 

Magnetite is present in fine grains, mostly of 

square outline, thickly· scattered throughout 

the section. It is for the most part of later 

growth than the three minerals just described. 

No inclusions of it are found in the augite or 

·olivine except along their margins, and very 

few are found in the biotite. ' 

·Apatite forms many small typical prisms. 

They appear to be mostly inclosed i:p. biotite, 

but many in the grolindmass may_ have been 

overlooked, owing to their close resemblance to 

the smailest augite crystals in transmitted 

light .. No pyrite was identified in this section, 

although the chemical analysis signifies the 

·presence of 0.24 per cent. 

Feldspar is present in places, forming a poikilitic matrix for the minerals ah·eady described. 

It occurs in divergent or radiating aggregates, 

as shown by its extinction, but each aggregate 

appears to be a homogeneous crystal in other 

respect~. :Its mean index of refraction is a 

little above 1.52 and, together with the dive!'ging habit, ·suggests albite. The isotropic 

gr.oundmass has an index of refraction a little 

above 1.51. In a few places it forms small 

rounded areas free frqm phenocrysts ~nd resembling an isotropic mineral such as analcite; 

but in some of these areas incipient growths of 

feldspar are recognizable, and no gelatinization 

was obtained. by evaporation with hydrochloric -acid. . The.re is no ~harp boundary 

between these rounded areas and the rest of 

the groundmass. 

· Chalcedonic quartz forms a few sm~ irregular aggregates in .the groundmass and is closely 

associated with calcite. 

SOUT~.IER:N" DIKE .. 

The southern dike, as seen in thin section, 

consists of ·phenocrysts of biotite, augite, 

apatite, and magnetite in a groundmass of 

feldspar which has a distinctly diverging or 

radiating habit. Alteration products are py.~ 

rite, calcite, chalcedonic quartz, chlorite, and 

hematite. 

In this rock biotite is more abundant than 

augite, constituting about 20 per cent of the 

section. It forms hypautomorphic crystals, 

the largest of ·which are not much over 1 milli-

,metei· in diameter. Its pleochroism, as a 

whole, is from ·medium brown to white. ·The 

borders of the crystals are darker brown than 

the main part. The central·p~rts of some crystals . are olive-colored. Alteration products, 

which are very scarce, include . calcite and 

chlorite. The biotite crystallized later than 

the augite. , 

· Augit.e forms hypautomqrphic grains, none 

more · than 1 millimeter long. The more 

prominent grains constitute about 5 per cen.t 

of the rock. Some grains show a little alteration to calcite, and some have fringes and veinlets of a very finely fibrous mineral, probably 

amphibole; 

Apatite forms prominent though small typical prisms; the largest 0.2 millimeter long. 

Magnetite is ·present only ·as fine grains of 

square outline, some of which ·are altered to 

hematite. · 

The. radiating feldspar which makes up· the 

groundmass has a mean· index of refraction a 

little 'above 1.52 and a large axi.al angle and is 

~ptically positive. These properties all inc}icate albite. No orthoclase was recognized. 

Little or no isotropic material is present in the 

groundmass. . 

Pyrite forms a few irregul.ar grains as much 

as 0.3 millimeter in diameter, which· may be 

impregnations of the grou:ridniass rather than 

primary crystals. 

Calcite; besides impregnating augite and 

biotite, forms a few small round t6 irregular 

aggregates impregnating the groundmass. Some 

of these are accompanied by chalced9nic quartz 

and some by pyrite. 

CHEMICAL COMPOSITION. 

The .chemical composition of the. northern 

(Santaquin) dike is shown by the a,nalysis in 

column 1 of the accompanying table, which 

includes also the most closely corresponding 

analyses given by W ashington. 1 

I Washington, H. S., Chemical analys_es of igneous rocks:· U.S. Gcol. 

Survey Prof. Paper 14, pp. 31.5-317, 1903. A second edition (Prof. Paper 

99) of this work has been issued since the completion of the pr~sent 

paper. · 
LAMPUOPHYR.E DIKES NEAR SANTAQUIN AND MOUNT .NEBO, UT'AH. 105 

Chemical analyses of lamprophyre from Santaquin, Utah, and rocks of similar composition. 

l 2 3 4 5 6 7 8 9 10 ll 12 

------11---1------------------------------

SiO.,..... 45. 59 45. 47 46: 67 · 48. 36 51. 68 48. 73 52. 09' 48. 66 44. 27 46. 47 49. 45. 50. 79 

Al 203 •••• 12. 02 13. 07 12. ()4 12. 42 14. 07 1i. 92 11. 93 · 12. 36 10. 73 15. 97 14. 41 15. 26 

Fe20i. . . . 3:84 6. 72 6. 13 · ·5. 25 4. 71. 4. 79 1. 84 3. 08 3. ·63 5. 97 3. 39 3. 2 9 

FeO...... 5. 05 12. 43 10. 17 2. 48 4. 57 / 4. 56 7. ll 5. 86 5. 87 4. 2.7 5. 01 5. 54 

MgO..... 7. 09 2. 80 · 5. 64 9. 36 7. 72 5, 93. 12. 48 8. 09 13.05 5. 87 8. 26 6. 33 

CaO. . . . . 10. 21 6. 79 11. 48 8. 65 6. 65 9. 24 7. 84 9. 97 10 .. 80 10 .. 54 6. 73 5. 73 

Na.llO.... l. 82 2. 04. L 64 l. 46 2. 45 2. 62 . 2. 04 2. 71 l. 07 l. 69 2. 54 3. 12 · :rev .. .'... 3. 90 3. 36 2. 31 3. 97 4. 16 2. 47' 3. 01 5. 15 4. 43 4. 83 4. 69- 2. 79 

iE8~:::: ~:g! ... ~--~~----~--~: .... ~·-~: .... ~--~~----~·-~~~------~~.} 1.46 3.23 2.32 2.43 . 2.74 

COA ...... ' l. 91 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. 80 . 16 . . . . . . . . . . . . . . . . . . . . . . . . . 61 2. 97 

'l'iv2 • • • • • 1. 67 . . . . . . . . . . . . . . . . 1. 18 1. 08 1. 34 . 73 . 97 1. 37 1. 33 1. 23 1. 02 

Zr02 ••••• None ..... 1 •••••••••••••••••••••• • ••••••••••••• : • ••••••••••••••••••••••••••••••••••••••••••••••• 

P~Or.·"· .. 1.33 .52 .74 .84 .72 .32 .34 1.07 .83 .73 1.12 .35 

M.n.O ... ;. . 16 . 21 . 19 . 13 Trace: . 36 . 15 . 13 . 06 . 01 . 13 . 07 

BaO..... . 20 . . . . . . . . . . . . . . . . . 29 . . . . ... . . 1'race. . .. ·..... . 40 .. 48 ....................... . SrO...... . 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 09 . 18 ................. · ...... . S..... . . . . . 13 .................. :. . . . . . 13 . 34 ......................... · ....................... · 0~ ••• • • Not det. . 28 . 34 Trace. . ............... · · . 10 .................. : .................... . N 10 . ·. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . ...... ·. .' 07 ..... ~ . . . . . . ... . . . .. ~ . . . . . . . . . . . . . .....•• Cl .............................................. : .11 ............................................... . J.,i20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . Trace. 'rrace. . .............................................. . ! 

Smn.... 100. 31 

Specific 

99. 85 100. 49 

2. a31. . 2. 703 

99. 93 100. 03 100. 05 100. 24 100. 00 100. 00 100. 00 100. 00 100. 00 

gravity. a 2. 755 2. 94 

a Apparent specific gravity. 'fhe apparent specific gravity of .the.southem (Mona) dike is 2. 680. 

l. Albite minette, Black Balsam claini, Santaquin, Utah. George Steiger, analyst. . . 2, 3. Basalt, Assab, near Massowa, Abyssinia. H.icciardi, L., Soc. geol. italiana Boll., vol. 5, p. 59, 1886. · 4. Absarokite, Clat·ks Fork, Yellowstone National Park. Iddings, J.P., Jour. Geology, vol. 3, p. 938, 1895; U.S. 

Geol. Survey Mon; 32, pt. 2, p. 329, 1899. · 5. Absarokite, Two Ocean Pass, Yellowstone National Park. Iddings, J. P., U. S. Geol. Survey Mon. 32, pt. 2, 

p. 329, 1899. . . 

6. Kersantite, Big Horn Pass, Yellowstone National Park. Iddings, J. P., U. S. Geol. Survey Mon. 32; pt. 2, · 

p. 70, 1899. 

7. Kentallenite, Glen Shira, Argyllshire, Scotland. ·Hill, J. B., and K.ynaston, H., Geol. Soc. London Quart. 

Jour., vol. 56, p. 537, 1900. · 8. Average shonkinite. Daly, R. A., Am. Acad. Arts and Sci. Proc., vol. 45, p. 228, 1910. 

9. Average misso.urite. Daly, H.. A., OJ:!· cit., .P· 229. 

10. Average leuc1te basalt. Daly, R. A., op. c1t., p. 229. 

11. Average minette. Daly, R. A., op. cit., p. 233 . . 12. Average kersantite. Daly, R. A.,· OJ.?. cit., p. 233. 

The ·noteworthy features of this an8lysis are biotite,. augite, and magnetite. The fact that 

low Si02 and relatively high alkalies, with. K20 the finely powdered rock is almost entirely 

in excess of Na20, which class ·the rock with picked up by a weak hand magnet is proof that 

alkaline varieties rather than normal basalt; little or no free ilmenite is present. The high 

also the high content of H20, C02, Ti02, and P20 5 · is at~ributable .to abundant apatite, 

P20 5 • The I-120 + is only in part accounted which is a characteristic feature of lamfor by biotite and the fibrous amphibole to prophyres and certain other rocks of similar 

which olivine is altered, and' the remainder is chemical composition. 

ev~dently present in the isotropic ground.rnass, Apparent discrepancies between the analy.sis 

partly in small bubble inclusions- and partly. and the mineral composition (mode) of the rock 

in solid solution. C02 is present in calcite, are the high CaO (about 6.5 per cent available 

whlch was introduced either at the close of for silicates), in contrast to the absence of 

· consolidation or somewhat later, at. the time calcic plagioclase, and the relatively high K20, 

of ore. depos.ition. · The Ti02 is definitely re- in. contrast to the absence of recognizable 

ferred to :fine rutile needles in biotite and is. orthoclase. In the calculation of' the mode, 

doubtless present as· a minor· component of however, the CaO is found to be just su.fficient 
106 SHORTER CONTRIBUTIONS TO GENE~~L GEOLOGY, 1918. 

to satisfy augite. The K20 in excess of that 

required by biotite evidently belongs to th~ 

glassy groundmass. . 

The difference between the norm and mode 

is shown below. The orthoclase in the norm 

includes the large quantity of K20 actually 

present in biotite, thealbite includes'the small 

quantity of N a20 in augite, and the anorthite 

-indudes much of' the. CaO and all of the Al20 3 

in augite~ The diopside and hypersthene and 

part. of the olivine, magnetite, .and ilmenit,e· in 

the norm are actually present in augite and 

biotite. 

Calculated mineral composition ~f lamprophyre dike at Santaquin,· Utah: Norm. Mode. 

Orthoclase. _______ ._ 22. 80 Orthoclase molecule~ 11. 12 

Albite. ______________ 15. 20 Albite. _______ -_--_-- 12. 05 

Anorthite. ___ . __ -.- __ 13. 34 

Diopslde. ___________ 14. 73 

Hypersthene. ___ ._._ 8. 85 

Olivine.____________ 3. 69 

Magnetite. ______ .... 

Ilmenlte ... ________ . __ 

Apatite ... _ _. __ -.- ___ _ 

Pyrite.---.------ ____ _ 

Calcite. ____________ _ 

Water ( +) __ · _______ _ 

Water (-). ______ . _. 

5. 57 

3. 19 

3:02 

. 24 

4. 30 

3.59 

1. 64 

Anorthite.· ________ · __ None. 

Augite._-.- __________ 35. 04 

Biotite. ______ ·_~ _____ 21. 27 

Olivine. ___ ......... l. 04 

Magnetite.____ _ _ _ _ _ _ 2. 78 

Ilmenite. _____ . __ . __ . . 91 

Apatite. _____ . __ ._.. 3. 02 

Pyrite. _____________ . . 24 

Calcite_ . ___ . __ . _ . . . . 4. 30 

Chalcedony---.-..... 3. 90 

Water ( +) unas- signed ____ . _ . _ _ _ _ _ _ 2. 83 

Water (-) ____ . _ _ _ _ _ 1. 64 

:MgO and FeO contents of biotite and augite. 

The rather high percentage of chalcedony is 

attributed to similar errors in the assignment 

of silica. 

Further evidence to confirm some of the 

foregoing statements was afforded by treating 

the. rock with strong hydrochloric acid and 

evaporating to dryness. The const~tuents dissolved are shown in th~ second column below. 

Partial analyses of constituents of lamprophyre dikes soluble 

in hydrochloric acid. 

Dike at Santaquin. 

Dike at 

Per Mona.: 

cent in Soluble Differ- Soluble com- 1

-n HCl. in HCl. plete . ence. 

analysis. 

Al20 3+ P20 5 .------ -·- 13. 35 

Fe20a--------------- &84 FeO _______ --------- _ · 5. 05 

MgO __ - _ - - - - - - - - - - - _ . 7. 09 CaO _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 10. 21 

Ti02 ---------------- 1.67 

092--------------- . 1. 91 

ro: 13 

7.42 

4.51 

5. 41 

. 95 

1. 91 

3.22 

2 .. 5.8 

4. 80 

:72 

. 00 

4. 10 

5.31 

4. 22 

5. 52 

. 51 

In the Santaquin dike there is on~y about 1. 9 

per cent soluble CaO in excess of that in calcite 

and ap·atite, and this may as well have come 

As no analyses of the .augite or biotite were. from slight corrosion of augite as from any 

made, the calculation of the mode is only undetected sodic · plagioclase. · The soluble 

approximate. ·The assume~ composition of magnesia is· mainly that derived from olivine. 

these two minerals is based on · a!lalyses of and biotite;. the iron from olivine, biotite, and 

augites and biotites f~om rocks that are magnetite; the titanic oxide from_ biotite and 

similar in composition to the . Santaquin magnetite. The alumina is derived largely 

lamprophyre. 2 According to this assumption from biotite, but· the proportion can not be 

the CaO no_t present· in apatite and c~~cite , told without determining the soluble alkalies. 

is exactly the amount required by the augite, The. soluble MgO and CaO indicate roughly the 

a cond~tion perfectly in accord with the ratio in augite, which. is only slightly less than 

optical character of the augite and the only that assumed· in the calculation of the mode. 

recognizable feldspar, albite. The· absence of Microscopic examination of the insoluble resimodal anorthite causes the ratios of Alz03 due showed it to consist mostly of augite and 

to K20 (1.9) in biotite and of Alz03 to CaO ·scales of isotropic silica left by biotite, with 

(0:30) in augite to be higher than the average sman amounts of albite, fibrous amphibole, 

for these minerals, but no higher than in ~orne . and glassy groundmass. 

of the analyses .tabulated by Cross, Iddmgs, The soluble portion of the dike near Mona 

Pirsson, and Washington.2 

agrees well with that of .the. Santaquin dike as 

. The low percentage. _of oliv~e in-_the m~de regards MgO and CaO. Its lower content- of 

compared 'to that estrmated ~ thin sectiOn Al2

0 3 and Fe203 is due in part to t~e incom- · 

is doubtless due to small errors m the assumed ·plete decomposition of biotite, shown by micro1 In glassy groundmass. scopic examination of the· residue, and perhaps . 2 Cross, Whitman, Iddings, J. P., Pirsso:ri, L. v., and Washington; in part to the greater ·insolubility of its thorH .. s., Quantitative classification of igneous rocks, tables 12 and 14, oughly crystallized feldspathic groundmass. 1903. 

• 
LAMPROPHYR.E PIKES N.EAR SANTAQUIN AND MOUNT NEBO, UTAH. 1Q7 

CLASSIFICATION. mass. A lamprophyre between minette and 

According to the quantitative classifict~tion kersantite, described by Schrader,S is desigthe Santaquin dike is designated by the coor- nated by the coordinates II.5.3:3 (shoshonose). 

dinates III.5.3.3 (kentallenose). The excess of These differences in classification show that the 

K.~O over N a20 is only a little lower .than that relatively few rocks sufficiently similar in min-· 

of III.5.3.2 (absarokose). According to its eral composition to be classed as minette _vary 

mode, it belongs to the minette-kersantite coi1siderably in relative ·amounts of chemical 

. group of lamprophyres. It differs from typical constituents. · · 

minette and kersantite, however, in possessing Ther"e is closer. agreement between -the 

a largely isotropic groundmass ruid in this re- Santaquin dike and three of the four inferior 

. spect res01nbles monchiquite or analcite basalt; analyses of minette tabulat~d by.Washington,6 

but the isotropic material has too high an index although these show considerably more Al20 3 • 

of refraction for analcite, is not readily· soluble, Co~pared with Daly's average of 10 analyses 

and does not gelatinize in hydrochlm:ic acid. of mmette 7 (column 12, p. -)the analysis 

The rock differs further from minette in con- ·of the Santaquin rock is rather low in Si02 and 

'taining no recognizable orthoclase or anortho- AlzOs, about normal in FezOs and MgO, high 

clase, although its mode shows that one or both in C~O,_ and .. ~rather low in alkalies, though 

of these 1ninerals would appear if crystallization simil3:r in theN azO-KzO ratio. .High H20 and 

were completed. It differs more markedly an~ Pz?s ar~ characteristic of se_veral rriinettes, · 

fro:m kersantite in the absence of a coilspicuous as 1s lugh T10z to a less. extent. . 

amount of anorthite molecule in the feldspar One a;nalysis of altered kersantite (column 6, 

and is best designated by the name vitrophy]:ic P· -) is very similar to that of the Santaquin 

"albite minette." ·The name "albite minette'' rock except in the ·ratio of N a20 to K20 and 

is equally applicable to the dike near Mona. in low PzOs. Most analyses of. kersantite, 

In chemical composition the Santaquin dike· ~o~vever, ~re higher in ~iOz and Al20 3 and lower 

differs considerably from the minettes repre- 1n uon ox1cles Mg\) and Ca0:8 · 

sented in the superior· ru1alyses ·tabulated by 

Washington.1 These are designated in the quan~ 

titmtive systen1 by IL5.2.3 (inonzonose), II.5.2.4 

(akerose), and II.5.3.2 (tlot named). They differ frotn the Sru1taquin rock in having higher 

Si02 and Al20 3 , lower Fe20 3 , FeO, and CaO, and 

two of the three~avelower MgO and higher N a20. 

·Of the 1ninettes analyzred since the publication 

of Washington's tables in 1903, a rock d·escribed by Ransome 2 is lower than the Santaquin rock in Si02 and Al20 3 an·d higher in K20, 

T'i02, and especially P 20 5 , corresponding to the 

. coordinates II.L6.1.2 (washingtonose).. Another min~tte, described by Cross,S resembles 

this one more closely' than the Santaquin rock. 

Of the analyzed mi1u~ttes described by Daly, 4 

two are desig11ated monz-onose and one 

III.5.2.2 (prowersose). Thf) latter, an olivii1ea.l.1gite minette, agrees with the Santaquin rock 

rather closely in percentages of Si02 , Al20 3 , 

N a20; ru1d K20, and in-having a glassy ground.,.· 

• Washington, H. S., op. cit., pp. 255, 263, 2G5. . 

2 Hansomo, 1~. L., An apatitic minette from northeastern 'Vashington: 

·Am. Jour. Sci., 4th scr., vol. 2G, pp. 337-339, 1908. 

a Cross, Whitman, D.iko rocks of tho Apishapa quadrangle, Colo.: 

U.S. Gcol. Survey Prof. Paper 90, pp. 18-20, 1915. . 

4 Daly, :n.. A., Geology of tho Nortil American Cordillera at tho fortyninth parallel: Canada Gcol. Survey Mem. 38, pp. 30~12, i912. 

S~MILAR ANALYSES OF OTHER ROCKS. 

Analyses 2, 3, 4, 5, and 7 in the table on page:-

represent other rocks which in some respects 

agree more closely with the Santaquin rock 

than the minettes and kersantites, whose 

analyses are given. · With the exception -of 

Nos. 2 and 3, which are termed basalt, the rocks 

represented by these analyses are the uncommon absarokite and km1tallenite. All except. 

·No. 4 (absarokose) belong to the subrang kentallenose. · The Santaquin rock differs from the 

absarokites in its abtmdance of biotite and from 

both absaro-kite and kentallenite in its lack of 

calcic plagioclase. 

Although single analyses of shonkinite differ 

in various ways from that of the Santaquin 

rock, falling ·in groups II.().2.3, III.6.1.1, andIII.6.2.3 of the quantitative system, Daly's 

aYerage analysis of shonkinite (column 8) is 

6 Schrader, F.·c., l\fineral dcpositsofthe Cerbat Range, Black Mountains, and Grand ·wash Cliffs, Mohave County, Ariz.:· U.S. Geol. ::;urvey 

Bull. 397, pp. 32-33, 1909. · 

a Washington, H. S., op. cit., p. 397. 

7 Daly, R. A., Average <lhcmical compositions of igneous rock types; 

Am. Acad. Arts and Sci. Proc., vol. 45; p. 233, 1910. 

s Washington, H. S., op. cit., pp. 227, 251, 259, 265, 2G9, 271, 281, 315, 

311, 411, 413. 
108 SHORTER CONTR.IBUT'IONS TO GENERAL GEOLOGY, 1918. 

very siD;lilar, as are his average analyses of regards ratio of feldspar, though high in fernie 

missourite and leucite basalt.1 The similarity minerals. 

of._ the minettes of the Highwood Mountains The isolation of the Santaquin d_ike from 

to the shonkinites of the same region was other intrusive rocks prevents more than gen-

. pointed out by Pirsson.2 The relatively low eral speculation regarding its origin, which 1nay 

· content of water, especially H20 +, in shonki- . be attributed, first, to a concentration of fernie 

_nites may be attributed in part to its escape constituents and normative calcic plagioclase 

.during relatively prolonged crystallization as in a monzonite magma; seCO!J-d, to conditions 

well as to fi·eedom from alteration. that caused the crystallization· of abundant 

-CORRELATION AND GENESIS. 

Minettes and kersantites are generally regarded . as 1nafic products, complen1entary to 

aphtes, of the differentiation of gra:qitic mid 

dioritic n1~gn1as and are found closely associated with large intrusive masses of these rocks. 

The nearest mass of post-OambJ:ian granite or 

granodiorite to Santaquin and Molila is about 35 

. miles to the north, in the Cottonwood and 

American Fork mining region/ and the only 

other intrusive mass within an equal distance 

is the monzonite stock of the Tjn tic mining district, 18 miles to the west.4 The fa.ct that the 

dike near Mona cuts Carboniferous limestone 

precludes correlation with the pre-Cambrian 

granite of the. Santaquin district. Correlation 

of the dikes with certain intrusive stocks is 

therefore impossible. As the Cottonwood and 

Tintic stocks, above mentioned, were intruded 

in Tertiary time, and as the e~x:tensive sheets of 

lavas in.central Utah 'yere erupted·in Tertiary 

tin1e, it is inferred 'that the two dikes also are 

of Tertiary· age. · 

The volcanic breccia in the Santaquin district 

is of latitic or andesitic character, as are the 

grea:ter part of the volcanic rocks to the west 

as far as the Tintic district: The only rhyolites of the region are closely !·elated to the 

monzonite and latite of the Tintic district in 

both occurrence and con1position. It seem13 

probable, therefore, · that the . two minettes 

under discussion are genetically related to a 

monzonitic magma represented by the latite 

breccias and flows of the region. 'rhe norni of 

the Santaquin dike (p. 106) ·is in~nzonitie as 

1 Daly, R. A., op. cit., pp. ~28, 2 29. 

2 Pirsson, L. V., Petrography a.nd geology of. the igneous rocks of the 

Highwood Mountains, Mont.: U.S. G~ol. Survey. Buli. 23-7,pp. 145-146, 

1905. 

a Butler, B. S., and L:mghlin, G. F., A reconnaissance af the Cottonwood-American Fork mining region, Utah: U. S. Geol. Survey Bull. 

.620, pp. 175-1'76, 1916. ' 

4 Lindgren, \Valdemar, and Loughlin, G. F ,, Geology and ore deposits 

of the Tintic mining district, Utah: U.S. Geol. Survey Prof. Paper 107, 

pp. 64-69 (in press). 

biotite and aluminous augite instead of less 

ah~·mino.us mafic minerals and calcic plagioclase. 

It may be assumed,·in accordanc~ with Bowen's 

hypothesis/ that at some stage in the period of 

monzonitic intrusions and eruptions parts of 

the n1agma undergoing gravitative differentiation became enriched in alkali~s; ''rater, and 

other volatile constituents, which both increased fluidity and lowered the tmnperatures 

of crystallization. Further differentiation ;was 

thus pron1oted, and separation of the heavier 

constituents continued. These· constituents 

1nay- have been re-dissolved to some extent by 

sinking to a depth where the· temperature was 

high· enough, thus forming a basic submagn1a 

rehitively high in alkalies and wate1~. Whether 

or not this happened, final crystallization took 

plac~ as follows: Olivine crystallized until the 

temperature became too low for it to exist in 

equilibriun1 with the magma; then, inst_ead of 

hypersthene, diopside, and calcic plagioclase, 

the more. con1plex mineral, augite, formed. 

Although augite contains very little water, the 

fact that it does not crystallize from dry fusions 

indicates that water and other volatile constituents of tl;le n1agma may have been the factors 

that determined its crystallization. The zonal 

character of the augite, showing an increase in 

content of alumina as it grew, is of interest in 

view of the absence of the anorthite molecule · 

in the feldspar of the rock. At still lower tenlperature biotite, a hydro~s mineral that prob~ 

ably contains fluorine, - crystallized, perhaps 

overlapping the period of later augite in -the 

ground1nass to some extent. After the larger 

biotite crystals had nearly attained their 

growth, 1nagnetite crystals begin to forn1; but 

the magma. solidified before they could attain 

any considerable size. 

The position of apatite in the order of crystallization is not so definite as that of any of the 

"Bowen, N. L., The late~ stages of the evolution of the igneous rocks: 

Jour. Geology, supplement to vol. 23, No.8, pp. 41-61, 1915. 
LAMPROPHYRE DIKES NEAR SANTAQUIN AND MOU~T. NEBO, UTA~. 109 

other minerals, owing to the Slnall size of its zation. Olivine is evidently unstable in their 

crystnls. 'rhey are clearly older than the large presence, even at high temper~tures .. Other 

. biotite crystals but are not found inclosed in minerals or glass in equilibrimn with thmn at 

olivine or augite. . · high temperatures are ·subject to attack by 

Crystalliza~ion of feldspar, partial in theSar{-:- them at low temperatures, and the long time 

taqujn di]re and complete in the Mona dike, sin.ce consolidation, supplemented by dynamic 

n1arked the :final stage of consolidatiqn. · Con- disturbances that ca:used fracturing, would 

siderable of the water and other volatile 1natter favor hydration and ·carbonatization. The 

not entering into biotite "ras retained in the presence of metalliferous deposits in· con,tact 

rock, either as m.i~1ute fluidal inclusions or d~s-: with or close by the Santaquin and ·Mona dikes 

solved in the glass groundmass. The retention leaves the source of water and carbon dioxide 

of water and other volatile matter may be an in their alteration products in doubt, but the 

· i1nportant :f n,ctor in· rendering lamprophyres . suggestion. may be worthy of consideration in 

especially subject to hydration and carbonati- the study ofother lamprophyres. 

0 

..