Brighan Young University Geology Studies

GEOLOGY I YOUNG STUDIES f UNIVERSITY Volume 12 December 1965 r' r' CONTENTS

Thrusting in the Southern Wasatch Mountains, Utah ...... Michael J. Brady 3

Nebo Overthrust, Southern Wasatch Mountains, Utah ...... B. Allen Black 55

Paleoecologic implications of Strontium, Calcium, and Magnesium in Jurassic rocks near Thistle, Utah .... Button W. Bordine 91

Paleoecology of the Twin Creek Limestone In the Thistle, Utah area ...... Ladell R. Bullock 121

Geolo of the Stockton stock and related intmsives, &1e County, Utah ...... John L. Lufkin 149

Stratigraphy and rifera of Ordovician rocks near Columbia Iceads, Jasper National Park, Alberta, Canada ...... J. Keith Rigby 165

Lower Ordovician conodonts and other microfossils from the Columbia Icefields Section, Alberta, Canada ...... R. L. Ethington and D. L. Clark 185

Publications and maps of the Geology Department ...... 207 Brigham Young University Geology Studies

Volume 12 - December 1965

Contents

Thrusting in the Southern Wasatch Mountains, Utah ...... Michael J. Brady 3

Nebo Overthrust, Southern Wasatch Mountains, Utah ...... B. Allen Black 55

Paleoecologic irriplications of Strontium, Calcium, and Magnesium in Jurassic rocks near Thistle, Utah .... Burton W. Bordine 91

Paleoecology of the Twin Creek Limestone in the Thistle, Utah area ...... Ladell R. Bullock 121

Geology of the Stockton stock and related intrusives, Tooele County, Utah ...... John L. Lufkin 149

Stratigraphy and porifera of Ordovician rocks near Columbia Icefields, Jasper National Park, Alberta, . . Canada ...... J. Kelth Rlgby 165

Lower Ordovician conodonts and other microfossils from the Columbia Icefields Section, Alberta, Canada ...... R. L. Ethington and D. L. Clark 185

Publications and maps of the Geology Department ...... 207 A publication of the Department of Geology Brlgham Young University Provo, Utah 84601

Ed~tor J. Keith Rigby

Editorial Staff Lehi F. Hintze Myron G. Best

Brzgham Your~gUniuerszty Geology Studres is published annually by the Department. Geology Studies consists of graduate student and staff research in the Department and occasional papers from other contributors, and is the successor to BYU Research Studies, Geology Serier, published in separate numbers from 1954 to 1960.

Distributed December 31, 1965

Prrce $4.00 Geology of the Stockton Stock and Related Intrusives, Tooele County, Utah*

JOHN L. LUFKIN Deparment of Geology, Western Mtchigan Urrrvers~ly,Kalamazoo, Mrrhrgan

ABSTRACT.-TheStockton Stock and related intrusives were mapped in an area approximately six square m~les,along the north wall of Soldier Canyon, in the west-central part cf the Oquirrh Mountains, Tooele County, Utah Samples were collected to determine mineralogy, method of emplacement, and metamorphic effects on Intruded formations. The Stockton Stock 1s a porphyritic adamellite intrusive that has invaded the lower Oquirrh Format~on. Related ~ntrus~vesinclude hypabyssal dikes and sills that are hypocrystalline and intermediate in composition. A bleached metamorphic aureole surrounds the stock and includes, in part, two facies of contact metamorphism: albite.ep~dotehornfels and hornblende-hornfels. Mining aaivlty flour~shedin nearby areas during the late 1800's and early 1900's. but how much ore was obtained from mlnes in this area 1s not known. Rush Valley District, adjacent to the mapped area, probably did not exceed $10,000,000 in total prcduct~on The economic future of the distr~ctdoes not appear to be great, due to the shallow nature of lntrusives, low rank metamorphism, and past hlstory of mining production.

CONTENTS

TEXT Economlc Geology ...... 163 page Development and History ...... 163 Acknowledgments ...... 149 References Clted ...... 164 Introduction ...... 150 Stratigraphy ...... 151 1I.LUSTRATIONS General Statement ...... 151 f ~gure Page M~ss~ss~ppianSystem ...... 151 1. Index map ...... 151 Great Blue Limestone ...... 151 Mississippian-Pennsylvanian System 154 plate Page Mannlng Canyon Shale ...... 154 1. Geologic map ...... 152-153 Pennsyl\-anian System ...... 154 2. Soldier Canyon Oquirrh Formation ...... 154 ...... following page 160 Quaternary System ...... 155 3. Sill Outcrops Structure ...... 155 ...... following page 160 Igneous Rocks ...... 155 4. Photomicrographs of Adamel- General Statement ...... 155 I~te,contact zone of Stockton Stockton Stock ...... 155 Stock ...... following page 160 Petrology ...... 157 5. Photomicrographs of contact Sills ...... 157 zonc Stockton Stock and dior~te Dikes ...... 159 s~ll...... following page 160 Summary of igneous activity ...... 160 table Emplacement ...... 161 1. Mineral composition of igneous Metamorphism ...... 161 rocks ...... 156

The writer expresses his appreciation to Dr. K. C .Bullock, thesis chairman, who suggested the problem, ass~sted in the field work, and constructively criticized the thesis writing. Thanks are also due to Dr. H. J. Bissell, who

'A thesls submrtted to the Faculty of the Department of Geology, Bngham Young Un~verslty In partla1 fulfillment of the requ~rementsfor the degree of Master of Sr~enre 150 JOHN L. LUFKIN supplied the aerial photographs; Burt Bordine, for helping measure sections, and Dr. Wm. Revell Phillips, who helped with the petrographic work.

INTRODUCTION In the early 1900's, most workers in the Oquirrh Mountains were concerned with mining activities centered around Mercur and Ophir Canyons and the famous Bingham porphyry copper deposits to the northeast. The first reconnaissance mapping in the thesis area was probably done by Paige of the U.S. Geological Servey in 1925. Gilluly (1932) continued Paige's work in 1926, publishing a geologic map of the Stockton-Fairfield Quadrangles on a topographic base of 1 :31, 250 scale. More recently, the area has been studied from a stratigraphic-paleoecologic standpoint. Moyle (1958) completed a thesis on paleoecology of the Manning Canyon Shale, measuring and describing the section exposed at the mouth of Soldier Canyon. Tooker and Roberts (1961a, b) have worked out the stratigraphy and structural geology immediately to the north. The thesis area constitutes the north half of Soldier Canyon, a prominent drainage on the west flank of the Oquirrh Mountains in west-central Utah (Text-fig. 1). This includes parts of Secs. 26-29, 32-35, T. 4 S., R. 4 W., in the northeast corner of the Stockton Quadrangle-. (Plates 1 and 2). The town of stockton, approximately four and one-half miles. northwest of the mouth of Soldier Canyon, is accessible both from the north and the south, via State Highways 36 and 73. The road leading from Stockton into Soldier Canyon is mainly an unimproved gravel road, which crosses Soldier Creek near the mouth of the canyon. The Stockton Stock and related intrusive bodies are located in the west- central Oquirrh Mountains (Plate 1). This mountain range trends north- south, rising steeply from Rush and Tooele Valleys on the west and Cedar and Salt Lake Valleys on the east. Gilbert (1890), Tooker and Roberts (1961b) have described a fault which borders the range on the west, thus associating this range with other fault-block mountains in the Basin and Range Province (Spurr, 1901) . Field work was done intermittently during the summer of 1964. The main concern of the writer was with the igneous and metamorphic rocks, which were mapped on an aerial photo base map, enlarged to a scale of 1"-1100'. Laboratory work included thin-sectioning collected samples and petrographic analyses, with the aid of a Universal Stage. Johannsen's (1931) System was followed, with minor deviations, in the classification of the igneous rocks. Under the heading of "Hypabyssal Rocks of Family 6"/7" ", Johannsen (1931, p. 310) states: "Corresponding to the porphyries, aplites, and pegmatite5 or normal granites, there are similar rocks belonging to the suite of the adarnellites, and called quartz-monzonites or adamellite-porphyries, -aplites and -pegmatites. In the present classification they ;\re not separated from the granitic and granodioritic hypabyssals, where they belong." The writer believes that since the bulk of the mapped igneous rocks are hypabyssal, porphyritic, and related to the Stockton Stock (an adamellite pluton), Families 6" and 7" of Johannsen's Classification should be referred to, although the letter "H" (hypabyssal) will be substituted, rather than the standard "E" (extrusive), or "P" (plutonic) notation. Thus, a STOCKTON STOCK 151

TEXT-FIGURE1.-Index map of the Stockton area, central Utah. porphyritic, hypabyssal rock, corresponding in mineralogy to Families 6" and 7" will be designated an adamellite, or adamellite porphyry. The classification of these rocks is based, in part, on their origin. A rock whose texture resembles an extrusive, with abundant glass, will be given [he rock name of the intrusive equivalent, that is, diorite instead of andesltr. Therefore, Johannsen's System will be followed, differing only to emphasize field occur- ance. STRATIGRAPHY General Statement Since the writer was concerned primarily with the igneous rocks of the area, the sedimentary rocks were not studied in detail. The following is a general summary of the stratigraphy.

MISSISSIPPIAN SYSTEM Great Blue Linestone The Great Blue Limestone crops out on the north side of the entrance to Soldier Canyon. Here, low dipping beds form a prominent cliff that strikes east-northeast. Farther up the canyon, the beds steepen to 70°. The unit is truncated on the west side by a normal fault, but continues eastward forming PLATE I

JOHN L LUFKlN 0 112 I MILE - - 1965 SCALE B. ALLEN BLSK - &i.MYoung Uaiversity Geology Studies - Vob12 1965

EXPLANATION SsQmentary Rocks

Aluvwm- Undividwi

OJd Alluvium

Cretaceous-Tertiory P'a~rllbtion Undivided

AdC9nslo Group 1

Jurassic- Undivided IT(u ( Nu@$$& Sandstone 1

&nkarah=I Formtion

Thuyncs=IW Limestone Triassic Undivided 1-1 Woodside Shale 1

fransonczl Member - Meade Peok Pork- City and Phosphoria Shale Tongue I Formatlons Undivided

Grandeur hlember-1

Dramottd Creek Sandstone u Kfrk'Srmon Limestone

Oqu3rrSI Formatton

Igneous Rocks pq Andesfte Dike

SYMBOLS

contact dash@@ where approximately locoted

U ---d Scuh in Miles Foult dashed where opproximotely located u, upthrown side; d, downthrown side

Thrust Fault dashed where opproximately located barbs on upper plate

Dip and Strike of beds of overturned beds of vertical beds +$

Anticline axis approximately located

Sy ncline axis approximately located

Paved Roads = Dirt Roods==== Quarries X Parmanent temp or or^ - Shrom s Streams GEOLOGIC MAP OF THE MOUNT NEBO-SALT CREEK VICINITY.

SOUTHERN WASATCH MOUNTAINS, UTAH Approximate Declination 16h0 EXPLANATION

SEDIMENTARY ROCKS IGNEOUS ROCKS SYMBOLS _ _-- u Contacts, interred. conceoled GRANITE u - - ...... 0 FouIII, inferred, conceoled 060 FAN GRAVEL AOAMELLITE .I-- u Strike and Dip Metomorphlc aureole OQUIRRH FORMATION MONZONITE PORPHYRY S Spring MANNING CANYON SHALE SILLS IUP-MONZONITE PORPHYRY --====zz==- - AP-AOAMELLITE PORPHYRY GREAT BLUE LIMESTONE 0-OIORITE UnimPr011d road

GEOLOGY OF THE STOCKTON STOCK AND RELATED INTRUSIVES

TOOEL€, COUNTY, UTAH JOHN L. LUFKIN a ridge along the south wall of the canyon. Only the upper part of the formation is exposed in the mapped area. Three members of the Great Blue have been recognized in the southern Oquirrh and Wasatch Mountains. The formation consists of a rather pure, basal limestone, a medial shale member (Long Trail Shale), and an upper silty limestone sequence. Baker and Crittenden (1961) have assigned this formation a Late Mississippian age. The writer measured 405 feet of the upper Great Blue Limestone at the mouth of Soldier Canyon. The section includes thin- to medium-bedded, dark gray to blue-gray, silty limestone, with laminated silt layers. Some of the beds are altered to a lavender color, and near the top, chert nodules are common.

MISSISSIPPIAN-PENNSYLVANlAN SYSTEM Manning Canyon Shale Manning Canyon Shale, Late Mississippian and Early Pennsylvanian in age, forms a crescent-shaped outcrop pattern along the north wall of Soldier Canyon, and then swings abruptly to form most of the canyon floor east of the coke ovens and south of Soldier Creek (Plate 1). This formation is also truncated by the same fault which cuts the Great Blue outcrop on the west. Gilluly (1932) named the Manning Canyon Shale from outcrops in Man- ning Canyon at the southeastern ti of the Oquirrh Range. Moyle (1958) designated Soldier Canyon as a re Perence section, since it is better exposed here than other known outcrops. Throughout much of the Oquirrh Range and the Wasatch Mountains, the Manning Canyon Shale is a valley former, as it is in Soldier Canyon. The formation is dominated by dark gray, brown, and black shales, with interbedded limestones, siltstones, and quartzites. Moyle (1958) measured a total thickness of 1559 feet in the map area. The writer placed the Manning Canyon-Oquirrh Formation contact at the base of a prominelit brown, thick- bedded quartzite unit. PENNSYLVANIAN SYSTEM Oquirrh Formation The Oquirrh Formation (Gillily, 1932) forms the thickest unit in the north Soldier Canyon area, as well as the rest of the Oquirrh Range. A partial section of moderate to steeply dipping beds is well exposed throughout most of the map area, with the best ex osures along the north-east trending ridges and spurs. A considerable part ofthe outcrop has been altered by intrusive bodies. West of the canyon mouth, the Oquirrh Formation crops out continuously north of the canyon road. The basal sequence, which is absent west of the canyon mouth due to faulting and erosion, is transitional with the underlying Manning Canyon Formation. The contact was mapped at the base of a local medium- to thick-bedded, brown weathered orthoquartzite. This formation is dominantly thin- to massive-bedded, gray limestones, with interbedded, brown weathering orthoquartzites, brown to black shales, and calcareous sandstones (Wells, 1963). The lower section is dominantly car- bonate, but in the northern part of the mapped area, brown to buff weathering, platy, calcareous sandstones and quartzites cap the mountain peaks. The writer has mapped the Oquirrh Formation as one unit, although Bissell (1959) has divided the formation into five time-rock members (with fusulinid zones), embracing most of the Pennsylvanian System in the southern Oquirrh Moun- STOCKTON STOCK tains. From oldest to youngest, these include: Hall Canyon Member (Mor- rowan), Meadow Canyon Member (Derryan), Cedar Fort Member (Des- moinesian), Lewiston Peak Member (Missourian), and Pole Canyon Member (Virgilian) . The exposed Oquirrh section was not measured by the writer in the map area, but includes several thousand feet of strata, largely the Hall Canyon and Meadow Canyon Members (Bissell, personal communication, 1965).

QUATERNARY SYSTEM Quaternary deposits consist mainly of Recent slope wash and valley alluvium, which are confined to the floor of Soldier Canyon and adjacent valleys, and talus slopes. One large deposit of coarse, unsorted limestone and igneous debris is located in Secs. 28-29, T. 4 S., R. 4 W., (Plate I), and is mapped as "old fan gravel". This distinction is based mainly on its position, thickness, and areal extent. No deposits of Lake Bonneville are found in the map area, since the lowest elevation is near 5500 feet.

STRUCTURE Throughout the area, the strata generally strike 60-70' N.W., and dip 50-60' N.E. This pattern is modified locally, by igneous intrusion and faulting. This area forms part of the southwest limb of the Pole Canyon Syncline (Gilluly, 1932; Tooker and Roberts, 1961b), which plunges to the northwest between Stockton and Tooele. At the entrance of Soldier Canyon, a major fault has truncated the Great Blue Limestone, Manning Canyon Shale, and part of the Oquirrh Formation. Gilluly (1932) mapped this fault (Soldier Canyon Fault) over two miles south, to the west flank of Bald Mountain, and has included it within the Basin and Range fault system. In Soldier Canyon, competent beds of the Great Blue Limestone show slickensides, brecciation, and dips of 65' westward into the fault zone, which has truncated the formation. These relationships suggest a normal fault, with the downdropped block of Oquirrh Formation on the west side, with dips of 12' to IT0, although marker beds are absent on either side. South of the area, the fault plane dips 50-60' to the west (Gilluly, 1932).

IGNEOUS ROCKS General Statement Most igneous rocks mapped in the area are hypabyssal in origin, including the Stockton Stock and numerous dikes and sills. The majority of these rocks are intermediate in composition and possess a porphyritic texture. These include adamellite (quartz-monzonite), adamellite porphyry, diorite, and altered equivalents. Each described igneous body is numbered on Plate 1, and is located by section number. Mineral composition and percentages are recorded in Table 1. Stockton Stock The major igneous body in the area is the Stockton Stock, which forms a linear outcrop pattern. The main mass is located in the SE 1/4 of Sec. 28, 156 JOHN L. LUFKIN

Table I.-- Mineral Composition by Percent of Igneous Rocks*

Or- orthoclase D- diopside Sa- sanidine Mg- maenetlte 01- ollgoclase Ap- apatite An- andesine Sp- sphene Qu- quartz Ep- epidpke H - hornblende kg- augite Bi- biotite Ca- calcite

+Glass percentage is not recorded. and projects into the SW 1/4 of Sec. 27, T. 4 S., R. 4 W., where it becomes very narrow. It is a little over one mile long, and is about 1650 feet wide, at its widest point. Where exposed, the contacts are sharp and generally concordant with the country rock. On the west end, where the contacts are best exposed, cross-cutting relationships are observed, particularly at the southern edge. The central area of the intrusive lies in a valley, and is largely covered by juniper and slope debris, but contacts are again visible on the eastern end of the stock. STOCKTON STOCK 157

Two distinct zones of the stock were mapped. Adamellite (quartz-monzonite) constitutes the major portion of the stock, while an aphanitic-porphyritic chill zone of granitic composition occurs on the northwest side in Sec. 28, T. 4 S.,. R. 4 W. Contacts between the two zones are not visible. The border zone has been more deeply eroded, and forms a saddle in the ridge. Petrology Samples of adarnellite show a light gray to pinkish gray color and are fine-grained. Visible minerals include light gray plagioclase, light pink orthoclase, quartz and dark green pyroxene. The rock is porphyritic with a hypautomorphic-granular texture. Pyroxene often occurs as irregular aggregates, rather than being evenly distributed. Essential minerals include oligoclase, orthoclase, and quartz (Plate 4, Fig. I). Phenwrysts of plagioclase are usually euhedral to subhedral, and reach 4 millimeters long, but are more commonly half this length. Zoning and twinning (albite and Carlsbad laws) are common. Orthoclase reaches a maximum of 2.2 mm.; zoning and Carlsbad twinning are common. Quartz shows normal development, and, together with orthoclase, forms the bulk of the groundmass. Biotite, magnetite, s hene, hornblende, apatite, and diopside constitute the accessory minerals ( fable 1). Diopside percentage classifies it as varietal. Orthoclase and plagioclase are usually altered to sericite and kaolin. Biotite and diopside, to a lesser extent, have been altered to chlorite. The border zone is a grayish brown, aphanitic-porphyritic granite, with limonite staining throughout (Table 1). Light gray orthoclase phenocrysts are conspicuous, some of which reach 1.2 cm. in diameter. Quartz is the only other megascopic mineral. Practically every mineral has undergone alteration in this rock. Orthoclase is altered to sericite and kaolin, particularly along fractures. Limonite commonly forms a halo around these phenocrysts, as well as other minerals. Plagioclase shows greater alteration, yeilding the same products. The abundance of calcite and chlorite suggests the previous existence of ferromagnesium minerals, although there is no direct indication. Most quartz grains are well rounded and show partial resorption.

Sills Two sills of similar composition crop out near the west-central border of Sec. 27, T. 4 S., R. 4 W., parallel each other and join at their eastern limits (No. S,). The lower sill (Plate 3, Fig. 2) is about 15 feet thick, and the upper sill is 20 feet thick. Both sills are hypocrystalline, and medium gray. Texturely, they are aphanitic-porphyritic. Light gray plagioclase, 2-3 mm. long, and dark hornblende are conspicuous in hand samples. The feldspars are altered to sericite and kaolin; chlorite is the main alteration product of the ferromagnesium- minerals. Contacts with the country rock are sharp and show no evidence of forceful intrusion. To the north, some limestones have been turned, in part, to marble, but this undoubtedly is related to the stock itself. Mineral composition of these sills is tabulated in Table 1. In the southeast corner of Sec. 27, T. 4 S., R. 4 W., (No. S,), a sill 30 feet thick crops out discontinuously for a distance of about 1640 feet. The sill is bordered top and bottom by a highly weathered zone 2 feet thick, which 158 JOHN L. LUFKIN

is in sharp contact with a fine-grained,- bleached limestone, now weathered to a cream color. This rock is a medium gray aphanitic-porphyritic intrusive. Thin-sections reveal a hypautomorphic-granular texture. Light gray phenocrysts of plagioclase reach 4 mrn. in length.- Other megascopic- - minerals include hornblende, biotite, and pyroxene. Plagioclase is usually subhedral to well-rounded. Zoning and twining are common in the plagioclase; sericite and kaolin are the main alteration products of feldspar, and biotite is altered to chlorite. Epidote, variety pistacite, makes up less than one percent of the rock, and is probably of hydrothermal origin. A hypocrystalline sill of dioritic composition crops out more or less continuously for over six thousand feet in Secs. 27, 34, and 35, T. 4 S., R. 4 W., (No. S,). It has a maximum thickness of 25 feet near its western limit, but thins to six feet on the east. Its contact with dark gray, fossiliferous limestone beds is sharp, showing no evidence of brecciation. Lower contacts of the eastern half of the sill have been weathered, giving a sharp separation of one- half inch with the country rock. The surface of the sill is weathered smooth, although slightly fractured. Joints are well developed, striking N. 42O E., with a dip of 85O S.E. Spacing between the joint planes varies from one to twelve inches. There appears to be no mineral orientation in samples from the western portion, but there is a definite hornblende orientation, parallel to the bedding planes, in samples collected from the eastern half. Dark gray limestone laminae are well preserved in these samples as well. Megascopically, the sill varies in color from a greenish-gray to pistachio green. Phenocrysts of feldspar (1.5 mm.) and hornblende (2-3 mm.) are conspicuous in an aphanitic groundmass. The sill may be arbitrarily divided into two suites of contrasting mineralogy and texture. In the western half, andesine microlites make up 80 percent of the total volume of the rock (Plate 5, Fig. 2). Hornblende forms euhedral to subhedral crystals, which are commonly twinned (100 as twin plane). Some has altered to chlorite. Epidote, which is characteristically anhedral else- where, forms euhedral to subhedral outlines in this rock. Calcite occurs primarily as inclusions. The texture is hyalophitic; microlites have a felty arrangement.- In contrast to the western half, the eastern portion shows a higher glass/ microlite ratio and a higher percentage of hornblende, much of which is oriented. Euhedral crystals include hornblende and sanidine. Other constituents are subhedral to anhedral. Epidote and hornblende are occasionally twinned. Calcite occurs both as inclusions and as an alteration product of epidote. Sericite and kaolin are the most common alteration products of feldspar. Quartz is anhedral and shows partial resorption. Two sills crop out continuously in parts of Secs. 33, 34, and 35, T. 4 S., R. 4 W., (No. S,). Both have been altered beyond classification, but appear to be of similar composition. The upper sill averages 25 feet thick, and is about 5500 feet long. Fossiliferous limestone beds, rich in brachipods and bryozoans, show no evidence of bleaching or brecciation. The lower sill is also about 25 feet thick, and is visible from the canyon road. It extends over one and one-half miles long. Both sills show the same general appearance, with light yellow, light brown, and rust-colored outcrops. Samples show a STOCKTON STOCK 159 relict porphyritic texture; phenocrysts of plagioclase (1-2 mm.) are well rounded and cream colored. Darker streaks parallel bedding planes. Lime- stone beds on either side do not appear to be altered, however, zones 10 to 20 feet on either side have considerable calcite fracture fillings, usually one to two inches thick running vertical to the bedding. The base of the lower sill is bordered by a breccia zone one foot thick, consisting mostly of angular limestone fragments, with 5-10 percent anhedral quartz interspersed throughout. Brecciation is not observed in the sill above. Microscopic study reveals the presence of quartz, orthoclase(?), plagioclase, magnetite and alteration products, including limonite, chlorite, and sericite. Limonite is found mantling at least 40 percent of the constituents, chiefly feldspar microlites. The groundmass consists approximately of 40 percent microlites, with minor glass. Quartz constitutes less than 5 percent of the rock. The two sills are most likely monzonite, or closely related, but no con- firmation can be made from thin-sections. In the northwest corner of Sec. 33, T. 4 S., R. 4 W., (No. S,), a sill 30 feet thick and approximately 1640 feet long has intruded the Manning Canyon Shale. The rock is weathered brownish-gray, with phenocrysts of feldspar (2-3 mm.) and biotite set in an aphanitic groundmass (Table 1). The microlitic groundmass (0.1-0.2 mm.) of feldspar is stained throughout by limonite. Orientation is not apparent, giving a felty texture. In addition to limonite stains, feldspar has been extensively altered to sericite and kaolin. Over 80 percent of the biotite has been converted to light green chlorite. Quartz occurs as anhedral aggregates, distributed randomly in the groundmass. Calcite occurs as rounded inclusions, commonly twinned. Sills exposed at location S, are very similar in composition to those exposed at location S,, and will not be further discussed here. Two other sills are associated with a dike in the central part of Sec. 29, T. 4 S., R. 4 W., and will be discussed under its description.

Dikes Four small, crosscutting intrusive bodies were mapped. In the northwest corner of Sec. 35, T. 4 S., R. 4 W., (No. D,), a crescent-shaped dike is exposed, over 400 feet long, and 65 feet at its widest point. Field samples are weathered medium gray in color, with phenocrysts of plagioclase (3-4 mm.) and biotite set in an aphanite groundmass. Forceful intrusion is evidenced by brecciation near its contacts, although not extensive. The rock is holocrystalline, with a hypautomorphic-granular texture. Plagioclase is commonly twinned and zoned, and altered to sericite and calcite. Subhedral orthoclase is commonly altered to kaolin. Biotite is usually euhedral, with inclusions of magnetite, although some fragments are strained and show embayments. Only a slight percentage has been altered to chlorite. Quartz is anhedral and evenly distributed in the groundmass. Calcite occurs both as inclusions, and to a lesser extent, as alterations of feldspar. A triangular dike, approximately 140 feet in diameter, has intruded the Oquirrh Formation in the northeast corner of Sec. 35, T. 4 S., R. 4 W., (No. D,). It is surrounded by a zone two feet thick of altered and brecciated wall rock, which grades outward through a bleached limestone zone of undetermined extent. Megascopic description is similar to the preceding dike, although darker gray, due to an increase in ferrornagnesium minerals, and a decrease 160 JOHN L. LUFKIN in plagioclase size. A phaneritic texture is visible. The rock is holocrystalline, with a hypautomorphic-granular texture. Euhedral phenocrysts of plagioclase are enclosed in a fine-grained matrix of orthoclase, quartz, and ferromagnesium minerals (Table 1). Maximum length of plagioclase is 2.1 mm., while some laths of hornblende are up to 1.3 mm. long. Hornblende is rarely twinned, and some fragments interpenetrate and are included in plagioclase. Other constituents show normal development. Secondary alteration products include kaolin, sericite, and chlorite. No calcite inclusions were observed, although undoubtedly present near marginal zones. In the south-central portion of Sec. 28, T. 4 S., R. 4 W., (D,), an elliptically-shaped dike outcrops within an extensively bleached and silicified area. It is approximately 825 feet long, and 200 feet wide. One prominent joint system strikes N. 3-18O E., and dips 71' W. Megascopically, the rock is a fine-grained, equigranular phanerite which has been extensively altered and stained yellow-brown by limonite. Black and bronze-colored biotite is the only visible mineral. Plagioclase is anhedral to subhedral, showing extensive sericitization. Minute sericite flakes are commonly oriented with the length of the crystals. Biotite is almost completely altered to vermiculite, chlorite, and limonite. Most of the orthoclase is anhedral and unzoned. Kaolin and sericite give it a speckled appearance. Quartz has subhedral outlines and is uniformly distributed. In the central portion of Sec. 29, T. 4 S., R. 4 W., three igneous bodies are exposed. These include a dike, and two sills of similar composition. The dike (No. D,) is deeply eroded and lies along a small saddle in a northeast- southwest trending ridge. Its north and south contacts are brecciated, but concordant with the country rock; its eastern margin is buried beneath old fan gravel. The extent of the bleached zone around the intrusive suggests that it widens out with depth. The rock has an aphanitic-porphyritic texture and is light to medium gray in color. Pink orthoclase (2-5 mm.), light gray plagioclase, and biotite are the megascopic minerals. Plagioclase is commonly euhedral. Sericite and kaolin have altered over 50 percent of its crystal surfaces. Orthoclase is subhedral, occurs both as phenocrysts and in the groundmass, and is altered primarily to kaolin. Some biotite fragments are bent, showing evidence of flow or strain; chlorite is often formed along biotite borders. Quartz outlines are anhedral to rounded, showing embayments due to resorption. Other samples collected from the same dike exhibit an equigranular, holocrystalline texture, are weathered to a cream color, and show limonite stains throughout. Except for the glass deficiency and the presence of limonite, these samples show approximately the same mineral composition and percentages. The bulk of the dike, however, has considerable percentage of glass.

Summary of Igneous Activity Based on igneous relationships within the mapped area, little conclusion can be drawn concerning the date of igneous activity. Most igneous rocks have intruded various sections of the Oquirrh Formation; no igneous masses were seen truncated by other intrusives. From this information, the activity would be dated as post-Pennsylvanian at the earliest. From regional considera- tions, however, the igneous instrusions are probably early Tertiary (Butler, 1920; Tooker and Roberts, 1961a, b). LXPLANATIONOF PLATE2 Photograph of north Soldier Canyon area. Soldier Canyon at far right. View looking east. PLATE 3 - JOHN L. LUFKIN

FIG. 1.-Typical outcrop of weathered sill 30 feet thick.

FIG. ?.-Jointed sill outcrop, 15 feet thick, in sharp contact with thin- to medium- bedded limestones of the Oquirrh Formation. PLATE 4 - JOHN L. LUFKIN -w

FIG. I.-Pliotoniicrograph of aclamellite, showing hypautomorphic-panular texture. Minerals include quartz (Q), orthoclase (Or), oligoclase (OI), and diopside (D). 3.5X. crossed nicols.

FIG. 2.-Photoniicrograph uf contact zone from southwest side of Stockton Stock. Diopside (D) zone forms sharp contact with adamellite intrusive on the right. 1OX, c~.ossed nicols. PLATE 5 - JOHN L. LUFKIN

FIG. 1.-Photomicrograph of contact zone from the northeast side of Stockton Stock. Minerals include oligoclase (01) , treniolite (T). and calcite (C) . I OX, crossed nicols.

FIG. 2.-Photomicrograph of diorite sill, showing subhedral crystals of hornblende (H) and epidote (E) in a groundniass of andesine microlites. lox, crossed nicols. STOCKTON STOCK 161

Emplacement The str~klngparallelism of the igneous rocks w~ththe strike of the sedl- mentary strata suggests that structural control, In part, was responsible for their emplacement. The sharp contacts, brecc~ationof wall rock, and orientation of the Stock- ton Stock suggest that both forceful intrus~onand the presence of a fracture zone were important ~n the emplacement mechan~sm dur~ngearly Tertiary. That many of the sills show sharp contacts, with little or no brecciation of sedimentary strata, suggests these were Intruded along fractures, although assimilat~on and replacement, part~cularly along the margins, certainly played a part. This is confirmed by samples showing well-defined rel~ct beddlng structures, with limestone lenses st111 preserved in the igneous rock.

Metamorphism Bleached metamorphic aureoles principally surround the Stockton Stock and two d~kesin the mapped area. The limits are particularly well exposed around the southern margins of the stock, and both north and south s~desof the dike (No. D,) in Sec. 29, T. 4 S., R. 4 W. These are the result primarily of contact, or thermal metamorphism, with 11ttle or no add~tlonof material from the magma source. Most sills did not produce metamorphic zones, due mainly to the~rlimited size and extent. The outer borders of these aureoles are sharp and show a marked color change from the unaltered wall rock. The extent of the aureoles is variable. The largest, of course, surrounds the Stockton Stock; the south margin extends over 1000 feet wide throughout most of its exposure. An unusually wide zone occurs around the d~ke~n Sec. 29, extending 1100 feet to the north, and over 1650 feet on the south. This wlde alteration zone suggests that the Intrusive contact flares outward with depth. Rocks of the contact zones include sil~ceousand calclc hornfels. They are typically very dense and fine-grained, varying from chalk white and gray to greenish-gray and dark green. Slllceous hornfels have resulted from bleaching of orthoquartzltes and sandstones. M~croscopically,these are even-grained wlth an average grain size of .04-.08 mm. Centers of quartz recrystall~zation are seen, showlng a rad~alstructure and undulatory extlnctlon. Siliceous hornfels closer to intrusive contacts show minute specks of magnetite radiating from a central point. Relict bedding is seen ~n many metamorphic zones. Contact of the southwestern tip of the Stockton Stock is very sharp, although ~t could not be followed along strike more than 30 feet. Hand samples show an inner, dark grayish green zone, less than one-s~xteenthof an inch wide. Moving away from the intrusive, Zone 2 is one-half inch thick, light gray-green in color, and very fine-grained, like the inner zone. Zone 3 is green~shgray, aphanitic, and grades imperceptibly into the sur- rounding bleached aureole through a few inches. Due to l~mitedextent, these zones were not mapped. The m~neralcomposition of these zones lncludes the following:

Diopside 99% Zone 1 Sphene less than 1% Epldote less than 1% JOHN L. LUFKIN

Diopside 65-35% Zone 2 Quartz 35-65% Sphene less than 1%

Zone 3 Quartz Diopside

Diopside found in Zone 1 is granular, with some prismatic crystals (Plate 4, Fig. 2). The average grain size is .08 mm. One or two fragments of anhedral epidote are located directly on the border of the intrusive. Sphene is subhedral and dispersed irregularly through the diopside groundmass. In Zone 2, moving away from the intrusive, there is a decrease in the diopside percentage and an equal increase in the quartz content. The size of the diopside grains remains about the same, but quartz sizes average .16 mm. Many anhedral quartz fragments show minute inclusions, probably diopside. Zone 3 consists mainly of interlocking quartz grains, largely recrystallized, with 6 percent granular diopside. Diopside is absent one foot from the contact with Zone 2. In summary, the aureole consists mainly of bleached quartzites and siliceous carbonates on the southwest side of the stock, except for the inner three zones just described. If a facies of contact metamorphism were ap lied to this particular contact, it would probably be included within the a1! ite-epidote hornfels. When this facies is developed, it usually occurs on the outer margins of aureoles, but it is often imperfect, due to low temperatures of metamorphism (Turner and Verhoogen, 1760). The northeast contact is more gradational and consists dominantly of calcite and tremolite, with minor grossularite, plagioclase, and quartz. (Plate 5, Fig. 1). The dimensions are approximately 20 feet wide and 200 feet along the strike. Approximately 10 percent of the rock consists of an unknown mineral, which has the following characteristics: low birefringence, low to moderate relief, no apparent cleavage, biaxial (-), with a 2V=54'. Some fragments are strongly zoned, with alteration zones of calcite and sericite. Because of its low percentage, the x-ray diffraction pattern of the mineral could not be determined. Hand samples are usually mottled shades of yellow-green and cream color, due primarily to the presence of tremolite and grossularite. The surface of one sample showed well developed dodecahedrons of light green grossularite, 2 mm. in size. As a whole, this contact zone was more brecciated and poorly defined, compared with the southwest contact zone. According to Turner and Verhoogen (1960, p. 514), this mineral suite is characteristic of the hornblende-hornfels facies, derived from the metamorphism of siliceous limestones. This facies develops within the temperature range of about 550' to 700° C., and a water vapor pressure (P H,O) of 1,000-3,000 bars. In summary, the metamorphic aureole around the stock is discontinuous and probably includes two facies: albite-epidote hornfels and hornblende- hornfels. The difference in the development of these contact zones is probably due to the difference in the intruded lithologic units, and possibly to variations in heat concentration throughout the stock. STOCKTON STOCK 163

ECONOMIC GEOLOGY Development and History Ten prospect pits, adits, and inclined shafts were located in the field. Most of the prospect pits were dug to a depth of five to ten feet. Generally, these are located on the tops of gossans, or "iron hats", or along limonite- stained breccia zones. Jasper, chert, and limonite form the bulk of material which was uncovered by hand tools. Inclined shafts, tunneled parallel to dip, and adits are abundant in Sec. 29, T. 4 S., R. 4 W., (Plate 1). Here, early prospectors tunneled near outcrops of igneous rock, or drifted into areas showing considerable bleaching of the sedimentary rock. Samples rich in hydrothermal specularite, with radiating structure were collected near the opening of an inclined shaft in the north- western part of Section 29. Most of the shafts and adits in the area have been caved, or boarded shut, which prohibited collection of samples. Although many Stockton residents could not recall recent activity in the area, one lease was posted in an adit, dated 1963. It stated that several thousand dollars were spent in re-evaluation of the claim; the name was not legible. Just east of the mouth of Soldier Canyon, an adit has been tunneled into the Great Blue Limestone, however, judging from the mine dump, little economic value was obtained. Little is known about the economic history in the map area, but the adjacent Rush Valley district, northeast of Stockton, had an interesting development. The following summary has been abstracted from Gilluly (1932), and Spurr (1895). The Rush Valley deposits were discovered in April, 1864, by soldiers of the Second Cavalry, California Volunteers. Most of the mining claims were just west of the map area, two miles north and south of Stockton. At that time, Stockton was a military post known as Camp Relief. The first discovery was called the Lincoln-a three-foot replacement vein carrying argentiferous galena in the Oquirrh Formation. The deposit was mined by two shafts, 100 feet and 50 feet in depth. The ore was 50 percent lead and 40 ounces of silver to the ton. Other mines in the same vein included the Tucson, Bolivia, Silver King, and St. Patrick. The mine that played the biggest part in the development of the district was the Honerine Mine, first located by General Conner in 1865, one mile northeast of Stockton. The ore included pipelike to tabular replacement bodies in the Oquirrh Formation. Hypogene ore minerals included pyrite, galena, sphalerite, and gold locally. Up to 1927, the total production was valued at $7,250,000 (Gilluly, 1932). Metals produced in the Rush Valley mining district were gold, silver, copper, lead, with minor zinc. Total value of ore mined from 1901-1917 is estimated to be $4,561,047 (Heikes, in Butler, Loughlin and Heikes, 1920).

Future The future of metallic production in the area is poor. Any ore that was mined was probably low grade, and the possibility for discovery of new deposits is remote, unless a core drilling program is initiated. This conclusion is based on the shallow nature of intmsives, lack of mineralization, and surface exposures. 164 JOHN L. LUFKIN

The purer, basal members of the Great Blue Limestone have been quarried south of the thesis area for utilization as a flux and also in the sugar-refining process. Outcrops of the Great Blue here are very silty and of local extent, and preclude its use in the previously named . purposes. . Manning Canyon Shale is being mined for clay in brick manufacture at several localities in Utah Valley. Should the supply for clay be depleted, the Soldier Canyon exposures may be a future site for development. The shale sequence has a limited exposure, but is quite accessible.

REFERENCES CITED Baker, A. A,, and Crittenden, M. D., Jr., 1961, Geologic map of the Timpanogos Cave Quadrangle, Utah: Geol. Quad. 132, U. S. Geol. Survey. Bissell, H. J., 1959, Stratigraphy of the Southern Oquirrh Mountains, Utah-Upper Paleozoic Succession: Guidebook to the Geology of Utah, no. 14, Utah Geol. Soc., p. 93-127. Butler, B. S., Loughlin, G. S., Heikes, V. C., and others, 1920, The ore deposits of Utah: U. S. Geol. Survey, Prof. Paper 111, 672 p. Gilbert, G. K., 1890, Lake Bonneville: U. S. Geol. Survey Mon. 1, 438 p. Gilluly, J., 1932, Geology and ore deposits of the Stockton and Fairfield quadrangles, Utah: U. S. Geol. Survey Prof. Paper 173, 171 p. Johannsen, A., 1931, A descriptive petrography of the igneous rocks: Univ. of Chicago Press, Chicago, Illinois, v. I and 11, 267 p. and 428 p. Moyle, R. W., 1958, Paleoecology of the Manning Canyon Shale in central Utah: Brigham Young Univ. Res. Studies, Geol. Ser., v. 5, no. 7, 86 p. Spurr, J. E., 1895, Economic geology of the Mercur Mining District, Utah: U. S. Geol. Survey 16th Ann. Report, Part 2, p. 370-455. ---- , 1901, Origin and structure of the Basin Ranges: Geol. Soc. Amer. Bull., v. 12, p. 247-270. Tooker, E. W., and Roberts, R. J., 1961a. Stratigraphy of the North End of the Oquirrh Mountains, Utah: Guidebook to the Geology of Utah, no. 16, Utah Geol. Soc., p. 17-35. ----, 1961b, Structural Geology of the North End of the Oquirrh Mountains, Utah: Guidebook to the Geology of Utah, no. 16, Utah Geol. Soc., p. 36-48. Turner, F. J., and Verhoogen, J., 1960, Igneous and metamorphic petrology: McGraw- Hill Book Co., Inc., New York, 2nd ed., 694 p. Wells, R. B., 1963, Orthoquartzites of the Oquirrh Formation: Brigham Young Univ. Geol. Studies, v. 10, p. 51-80.

Manuscript received May 27, 1965