MARIAN B. JACOBS Larnont Geological Observatory, Columbia University, Palisades, N. Y. PAUL F. KERR Dept. Geology, Columbia University, New Yor/{, N. Y.
Hydrothermal Alteration Along the Lisbon
Valley Fault Zone, San Juan County, Utah
Abstract: The Lisbon Valley fault follows a north- Rocks along the fault zone have generally been west strike along the crest of a salt anticline and bleached, and porous Burro Canyon Sandstone has cuts diagonally across the Big Indian Wash uranium been sihcified for 50 or more feet away from the area in San Juan County, Utah. Altered rocks col- fault on the hanging-wall side. Solution activity lected along the fault zone have been studied in the fault zone is indicated by bleaching, silicifi- microscopically and by X-ray diffraction, for cation, and deposition of copper sulphides. Argilhc significant mmeralogical data with a bearing on mineral associations and indurated hydrocarbons mineralization. indicate that the mineralizing solutions were heated. Abundant kaolin is found in altered Chinle strata The western upthrowu limb of the Lisbon Valley near the fault and extending 50 to 300 feet away. anticline contains uranium deposits which occur In contrast, illitc, chlorite, montmonllonite, and mostly in Triassic Chinle Shale, but also in Permian mixed-layer illite-montmorillonite arc commonly Cutler strata. The rising thermal mineralizing solu- found in unaltered Chmle Shale occurring else- tions active along the Lisbon Valley fault zone may where along the Lisbon Valley anticline. Veinlets have carried uranyl ions which were reduced and of dickite occur in the zone of shear, accompanied precipitated in Chinle strata. The passage of solu- by tiny veinlcts of pyrite and globules of indurated tions to the Chmle most likely followed subsidiary asphalt. Both original copper sulphides and oxidized fractures and certain porous beds found in the copper minerals occur in fractured rock along the Permian Cutler Formation, known as sugar sands Lisbon Valley fault over a wide stratigraphic range. in the mining localities.
CONTENTS
Introduction 424 3. X-ray diffraction patterns of dickite and Acknowledgments 424 kaolimte, American Petroleum Institute Geologic setting 424 reference material 430 Stratigraphy 424 4. X-ray diffraction patterns of dickite filling Structure 424 white veinlcts of Lisbon Valley fault zone, Alteration and mineralization of the fault : 425 samples 52, 58, and 54, North Alice incline 432 Laboratory observations 427 5. Thin section sketch of vemlet filled with pyrite Specimens examined 427 and dickite in shear zone (specimen NA 58) 434 Technique 427 Bleached and unbleached Chinle Shale . . 428 Plate Mineralized shear zone 429 1. Silica occurrences near Lisbon Valley fault, Matrix 429 Utah 432 Veinlets 429 2. Mineralized gouge and shear zone specimens, Associated minerals 43? Lisbon Valley, Utah 433 Burro Canyon alteration 433 Big Indian copper-bearing strata .... 434 Blackbird copper-bearing strata 434 Table Significance of dickite occurrence . . . . 435 1. Stratigraphic sequence in the Lisbon Valley Summary and conclusions 437 area, Utah 424 References cited 438 2. Matrix minerals in specimens from Lisbon Val- ley fault zone, Utah 427 I'igurc 3. X-ray diffraction d-spacing and intensity mea- 1. Index and location map for Big Indian Wash surements for untreated and heated kaolin- uranium district, Utah 425 ite 428 2. North Alice incline section across Lisbon Valley 4. X-ray diffraction d-spacing and intensity mea- fault with sample locations 426 surements for untreated and heated dickite 431
Geological Society of America Bulletin, v. 76, p. 423-440, 5 figs., 2 pis., April 1965 423
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helpful in discussion of general geological fea- INTRODUCTION tures. The study has been made possible by the Southeast of Moab, Utah, the North Alice support of the Division of Research and the uranium mine and several abandoned copper Division of Raw Materials of the United States mines are located along the Lisbon Valley fault. Atomic Energy Commission. A 20°-inclined shaft cuts through the fault and provides excellent exposures of a structurally GEOLOGIC SETTING significant area. Slopes intercept the fault in several places within the North Alice mine. Stratigraphy Surface outcrops at the northwest edge of the Table 1 (after Lekas and Dahl, 1956) out- Big Indian open pit and at the Blackbird cop- lines the stratigraphic units in the immediate
TABLE 1. STRATIGRAPHIC SEQUENCE IN THE LISBON VALLEY AREA, UTAH
System Series Formation Thickness m ieet Dakota Ss. Cretaceous Lower and 20 Burro Canyon Fm. — Ijnt'ofiformi/v — Brushy Basin Sh. 450 Salt Wash Ss. 325 Upper — Unconformity — Summerville Fm. 10-100 Jurassic Entrada Ss. 170 Middle Carmcl Fm. 60 Navajo Ss. j 170-320 Lower Kaycnta Fm. 230 Wingate Ss. 280-360 Tnassic Upper Chinle Fm. 340-480 — Unconformity — Pennian- Cutler Fm. Pennsylvaniau Rico Fm. 1470 Pennsylvanian Hermosa Fin.
per pit also provide information on alteration vicinity of Lisbon Valley. Mudstones and along the fault. shales of the Triassic Chinle are in fault con- The fine-grained alteration minerals from the tact with the Cretaceous Burro Canyon Sand- Lisbon Valley fault zone have been studied stone where the North Alice incline crosses the with a Norelco X-ray difiractometer and in Lisbon Valley fault. The Triassic Moenkopi fragments and thin sections with the polarizing Formation is absent from the Lisbon Valley microscope. X-ray diffraction patterns of area, so that the Permian Cutler Formation is alteration clays were run with Ni-filtercd Cu unconformably overlain by upper Triassic radiation (X = 1.5418A) at 40 kv, 17 ma po- Chinle shale. tential, scanning speed of 1° 2d per minute, with 1° and 0.003" slits, and a 17-cm goni- Structure ometer radius. The Lisbon Valley anticline and fault (T. 29-30 S., R. 24-25 'E.) determine the struc- ACKNOWLEDGMENTS tural trend (Fig. 1) ol the immediate area (Dix, The co-operation of Mr. Gordon Minor, 1953; Lekas and Dahl, 1956; W. B. Loring, Mr. Walter Weid, and other members of the 1958, Ph.D. thesis, Univ. of Arizona). The Homestake Mining Company staff in connec- anticline represents a salt uplift with a north- tion with this study is greatly appreciated. We west alignment typical ot the Paradox Basin, thank Mr. Harold Blakley'and Dr. William although the salt does not pierce the overlying Loring of Atlas Minerals who have been most formations. The fault breaches the crest of the
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anticline, with the downthrown side on the 20 to 30 feet wide with extensively brecciated northeast. At the Big Indian mine the fault rocks, marks the fault. Fractures in shear zone plane dips 58° northeast. A maximum throw rocks are filled with pyrite, clay, hardened of 4000 feet (Lekas and Dahl, 1956, p. 162) asphalt, copper sulphides, and oxidized copper attests to the significance of the dislocation. minerals. Specimens of Chinle Shale from this The La Sal Mountains, 8 miles north of Lisbon zone are highly fractured and traversed by a
Figure 1. Index and location map for Big Indian Wash uranium district, Utah. (Modifiedfrom U. S. Atomic Energy Commission Preliminary Map No. 3, 1956)
Valley, are laccolithic intrusions into the north- network of minute white veinlets. Chinle rocks west-trending belt of salt anticlines. are bleached for a few feet from the shear zone on the foot-wall side; a short distance farther, Alteration and Mineralization of the Vault 7.one unbleached red shales occur (Fig. 2, modified Alteration effects as exposed along the North from Kerr, 1958, p. 1099). On the hanging- Alice incline were reported in a preliminary wall side, the Cretaceous Burro Canyon Sand- manner by Kerr (1958). A broad shear zone, stone as exposed in the North Alice incline is
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extensively silicified, tapering and interfinger- are the major sulphides and covellite and chal- ing with less siliciiied sandstone away from the copyrite are less common; tenorite, cuprite, fault zone. and native copper are widespread in trace COPPER: Concentrations of copper minerals amounts (Weir and Puffett, 1960, p. 137). occur on the hanging wall of the fault, in sand- Massive chalcocite with bormte traversed by stones and conglomerates of the Dakota-Burro calcite-filled fractures has been collected along Canyon Formation. Copper has been mined in the fault zone in the North Alice workings. the Big Indian mine at the northwest end of The ore minerals fill interstices, coat grains, re- the anticline, in the Blackbird mine to the place fossil plant material, and fill fractures southeast, and in several small prospects along ranging from microscopic cracks to faults with the fault. Farther southeast of the Big Indian a few inches displacement.
Figure 2. North Alice incline section across Lisbon Valley fault with sample locations. (Modifiedfrom Kerr, 1958)
Wash district, in a study of the Mt. Peale 4SE URAXIUM: Uranium ore has been mined on quadrangle, Weir and Puffett (1958) observed the hanging-wall side of the fault from Jurassic carnotitc, vanadium mica, malachite, azurite, Morrison strata (Salt Wash) at the Rattlesnake and chalcocite in the Burro Canyon Formation open pit. In the upthrown footwall of the fault, near a fault at the Lucky Strike adit near the uranium ore occurs in Triassic Chinle strata northwest corner of the quadrangle. Both the (Moss Back) and is mined in the North Alice uranium and vanadium minerals are localized workings, where the ore may be found in places along joints. The copper deposits in the Mt. in contact with the fault. Uranium ore is mined Peale 4SE quadrangle are small. in numerous localities in Chinle strata whose According to Weir and Puffett (1959; 1960) arcuate outcrop outlines the footwall-side of most copper ore has come from the late Cre- the Lisbon Valley anticline. To the southeast, taceous Dakota Sandstone, but other occur- the Lisbon Valley fault again terminates the rences are in the Pennsylvanian Hermosa, Per- outcropping Chinle strata, and near the fault, mian Cutler, Triassic Chinle, Jurassic Kayenta the uranium-producing Divide and Continen- and Morrison, Cretaceous Burro Canyon, and tal workings are found. Minor occurrences of in Tertiary brecciated igneous rocks in the La uranium- and vanadium-bearing rock have been Sal Mountains. The deposits have yielded more found in Cutler strata truncated by the Tri- than 150,000 tons of ore averaging 1.4 per cent assic-Permian erosional surface, with copper copper. deposits in the lower part of the Cutler Forma- Malachite, azurite, and brochantite are the tion and in the Cretaceous Burro Canyon For- principal ore minerals; chalcocite and digcnite mation (Weir and Puffett, 1959, p. 9).
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SILICA: Silicification has been observed on Triassic in the North Alice mine (PI. 1, fig. 2). the surface near the Lisbon Valley fault, along Chalcedony occurs as small nodules and string- fractures, and in massive impregnations of ers replacing sandstone in uranium ore bodies, coarse sandstone or conglomerate, such as a as well as in barren strata not more than a few knob 20-30 feet in diameter immediately south- hundred feet from ore. Chert is also found in east of the access road leading to the Big Indian Cutler strata on the western escarpment of Big
TABLE 2. MATRIX MINERALS IN SPECIMENS FROM LISBON VALLEY FAULT ZOXE, UTAI;
Occurrence Number Description Matrix minerals Chinlc Shale Unbleached Red with light-green Kaohnite, mixed-layer ilhte- mottling montmorillonite, hematite Red with white veinlets Kaolimte, mixed-layer illite- montmonllonite, hematite Bleached Green clay with white Kaolinite, mixed-layer illite- veinlets containing black montmorillomte, pyrite disseminations 59 Gray-green with red Kaolinite, mixed-layer illitc- carbonate in slickensidcs montmorillonitc 63 Mottled red-green clay Kaolinite, mixed-layer illite- showing slickensides montmorillonitc Hrokcn and mineralized 54 Light gray clay with white Dickite, kaolinite, mixed-layer shear zone veinlets and numerous illite-montmorillonite, disseminated black spots asphaltite, pyrite 58 Gray clay veined with Dickite, kaolinite, mixed-layer pynte and white clay ilhte-inontmonllonite, and containing lustrous asphaltite, pyrite black disseminations 199 Fractured gray clay with Dickite, kaolinite, mixed-layer white veinlets and black illite-montmorillonite, disseminations asphaltite, pyrite Gouge zone in hanging 52 Fractured gray-green clay Dickite, kaolinite, mixed-layer wall with white veinlets and illite-montmorillonite, orange and violet staining asphaltite Sheared and altered 53 White quartzitc with Chalcedony Burro Canyon Sandstone limonite staining 198 Limonite-stained silicified Kaolinite, chalcedony, jarosite conglomeratic sandstone Silicified Burro 57 White silicified sandstone Chalcedony Canyon Sandstone 62 White quartzite Chalcedony Unaltered Burro 56 Less silicified white sandstone Kaolinite, chalcedony Canvon Sandstone 61 with limonite staining
mine (PI. 1, fig. 1). In the North Alice incline, Indian Wash several miles southeast of the Burro Canyon Sandstone has become cemented North Alice workings. by silica into a quartzite at the fault zone. At the Lucky Strike mine to the southeast, silica LABORATORY OBSERVATIONS was introduced along fractures paralleling the Lisbon Valley fault (Weir and Puffett, 1960, Specimens Examined p. 140). Copper deposits occur in altered brec- Table 2 describes argillic specimens and their ciated dionte porphyry in the La Sal Moun- essential minerals, collected from the North tains. The diorite porphyry is argillized and Alice incline at the Lisbon Valley fault zone. silicified, with silica deposited in small vugs formed by destruction of phenocrysts (Weir Technique and Puffett, 1960, p. 141). Laboratory studies have consisted essentially Lenses of red chalcedony may be found on of X-ray diffraction investigation of matrix the erosional surface between the Permian and clays coupled with optical investigation of thin
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sections and fragments. To separate argillic standard practice, adsorption and dehydration matrix materials, each sample was lightly properties were used to aid in identification of ground, immersed in distilled water, and placed the fine layer lattice clay aggregates. in a Waring blendor to disaggregate the par- ticles. After disaggregation and settling, the Bleached and Unbleached Chinle Shale finest fraction was sedimented on glass slides, The matrices of Chinle red shale specimens so that basal (001) cleavage surfaces oi layered from unbleached strata on the upthrown side of silicate minerals would be oriented parallel to the Lisbon Valley fault contain clav minerals
TABLK 3. X-RAY DIFFRACTION D-SPACING AND INTENSITY MEASUREMENTS FOR UNTREATED AND HEATED KAOLINITE Random orientation; i = illitc; in = montmorillonite; q = quartz; f = feldspar; k = kaolinite
Murfreesboro, Arkansas Green clay (Spcciinen NA 59) from Lisbon \ alley A.P.I, la fault zone, Utah Untreated Untreated 1 leated dA Irel. dA Irel. dA I rcl. 11.62 ~l 11 10.64 i,m 12 10.04 i 10 9.93 J H 9.50 m 6 7.H (001) 100 7.13 k 31 * 4.870 i 7 4.979 i 4 4.458 32 4.458 k 24 4.480 i 21 4.350 70 4.350 k 15 * 4.247 q 44 4.267 q 37 4.168 65 4.168 k 12 * 3.831 43 3.831 k 11 * 3.736 20 3.720 9 * 3.574 (002) 93 3.574 k 40 * 3.373 20 3.336 q 100 3.349 100 3.241 f 33 3.162 6 3.162 k 11 * 3.108 8 3.087 i.rn.k 9 3.087 i,m 6 2.744 7 2.568 i 17 2.576 i 8 2.554 25 2.554 k 18 * 2.533 24 2.520 k 8 * 2.493 33 2.490 k 7 * 2.453 q 23 2.459 q 14 2.383 (003) 12 2.377 k 7 * 2.336 52 2.336 k 9 * 2.290 32 2.279 q,k 17 2.279 q 10 2.235 q,i 10 2.235 q,i 8 2.186 4 2.184 k 5 * 2.125 q 14 2.125 q 10 1.987 13 1.979q,i,k 9 1.979q,i 7 1.941 6 1.839 4 1.815 q 27 1.819 q 17 * Kaolinite lattice destroyed 1 Indicates broad peak.
the surface of the slide. X-ray diffraction pat- similar to the gray-green specimens found in terns were taken of three fractions for each the bleached zone: kaolinite, mixed-layer illite- specimen: (1) the untreated sample, (2) the montmorillomte, and, in some, small quanti- sample after being sprayed with a light mist of ties of illite and chlorite. Bleaching, produced diethylene glycol monobutyl ether, and (3) the by the removal of iron oxide pigment, appears sample after heating for 2 hours at 550°C + to constitute the most apparent difference be- 10°C in an electric furnace. Thus, according to tween the two zones.
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Heating for two hours at 550°C dehydrates portion of the main shear zone (PL 2, fig. 1), kaolinite and destroys its crystal lattice, as may exposed in the North Alice incline, exhibit a be observed on X-ray diflraction patterns of marked increase in kaolin content in contrast both red and bleached gray-green Chinle Shale. to the amount in unaltered and bleached Chinle X-ray data for kaolinite in a North Alice speci- specimens. A similar increase is shown by frac- men have been compared with similar data on tured green clay with white veinlets from the kaolinite from Murfrccsboro, Arkansas, to gouge zone of a small fault in the Burro Canyon verify the identity of the somewhat impure (PI. 2, fig. 2) of the downthrown area. The in- aggregate (Table 3). Lines attributed to crease in kaolin content is on the order oi two kaolinite in the unheated material disappear on to three times, relative to the mixed-layer clay heating, whereas those caused by quartz, illite, component as shown by a comparison of the and collapsed montmonllomte remain. North amplitudes of the 7 A and 3.5 A reflections to Alice incline Chinle samples indicate that ka- the 11 A peaks. The altered materials from the olini/.ation extends outward intermittently 50- mineralized shear zone also show small quanti- 300 feet Irom the Lisbon Valley fault zone and ties of mixed 10 A nonexpanded and 12 A ex- is not encountered in more distant reaches, ex- panded layers which produce a rellcction be- cept for small amounts in certain porous, tween 10.5-11.5 A. bleached Cutler strata (known locally as sugar Veinlets. Further examination of the min- sands) when they occur close to the fault /.one. eralized shear zone specimens reveals that the The mixed-layer illite and montmorillonite 7 A and 3.5 A reflections belong to two kaolin observed in these specimens yields a (001) members, kaolinite as found in altered zones spacing at 11-11.5 A, which splits on glycola- surrounding the fault, and, where alteration is tion to two peaks between 9-10 A and 12-13 intense, dickite in veinlets (Pi. 2, figs. 1 and 2). A and collapses on heating to an intense peak The two minerals were initially identified by in the 10 A region, similar to a mixed-layer X-ray diffraction patterns obtained before and clay studied by Weaver (1958). These spacings after heat treatment to 550°C. Unlike ka- suggest that the mixture consists of 10 A and 12 olinile, the pattern given by dickite persists on A layers, with the resulting peak at an inter- heating until above 600°C (Molloy and Kerr, mediate value of 11-11.5 A. When glycolated, 1961). This mineral is generally found as the two high-angle peaks form as a result of a high-temperature member of the kaolin family. 10 A/17 A and a 10 A/8.5 A combination. The After heating to 550°C, the pattern of kaolinite intermediate values observed approach the end is totally destroyed, while dickite peaks are limits as the concentration of expanded layers only slightly reduced. This essential difference increases. When compared to Weaver's (1956, in dehydration temperature is illustrated in p. 207) patterns of mixed-layer clays, the d- Figure 3 by American Petroleum Institute ref- spacing values observed in the altered and un- erence material 15a (dickite from San Juanito, altered Chinle specimens suggest the presence Chihuahua, Mexico) and la (kaolinite from of about 30-40 per cent expanded layers in the Murfreesboro, Arkansas); and in X-ray diffrac- mixture. tion patterns given by Molloy and Kerr (1961). Thin sections of bleached Chinle show a silty Other differences observable in the diffrac- shale with a matted light-brown clay ground- tion patterns of the two minerals are sharpness mass and small irregular grains of detrital quartz of pattern and slight differences in d-spacings and feldspar. In places feldspar grains arc ob- and intensities. The (002) reflection of dickite served in several stages of alteration to clay, may tend to a slightly higher value: 3.58 A for and opaque square cross sections of pyrite are dickite (Table 4) and 3.57 A for kaolinite disseminated throughout the fine-textured ma- (Table 3). The three reflections preceding the trix. Unaltered Chinle Shale exhibits extremely (002) line of the unoricntcd pattern also show fine-grained clay material colored deep red observable differences in d-spacing and in- brown by iron oxide pigment and identified by tensity: X-ray diffraction as hematite. Tiny black in- clusions of asphalt surrounded by halos which Kaolinite Dickite lack red pigment are present; these suggest the (hkl) d A I rel. (hkl) d A I rel. effectiveness of the hydrocarbon as a reducing (Ill) 4.17 65 (1U) 4.14 44 agent. (021) 3.83 43 (112) 3.95 11 (021) 3.74 20 (022) 3.80 17 Mineralised Shear Zone The patterns and values shown (Fig. 3; Tables Matrix. Specimens from the mineralized 3 and 4) illustrate these differences, which agree
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DICKITE
UNTREATED
3.5 4 10 17 ANGSTROMS
Figure 3. X-ray diffraction patterns of dickitc and kaohmtc, American Petroleum Institute reference material. (Random orientation.) The dickite is from San Juanito, Mexico, and the kaolmite is from Murfrccsboro, Arkansas.
with the illustrations and tables given by Mol- kaolinite this line occurs at 3.37 A, and in loy and Kerr (1961), by reference dickite speci- dickite, as^two lines close together, at 3.46 A mens (Reference Clay Minerals, A.P.I. Re- and 3.42 A, sometimes appearing as a broad search Project 49, 1951, Prelim. Rept. NTo. 7), peak. and by Brown (1961, p. 111-115). Both kaolinite and dickite occur in the min- The line immediately following the (002) eralized shear zone specimens in varying reflection in unoriented patterns of dickite and amounts. The reduction in intensity of 7 A and kaolinite also aids in distinguishing X-ray dif- 3.5 A peaks after heating indicates collapse of fraction patterns of dickite from kaolinite. In kaolinite reflections and emergence of remain-
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ing dickite lines. The patterns obtained after X-ray diffraction patterns of untreated speci- heating^ show an apparent shift of (002) to mens yield d-spacings characteristic of dickite, 3.588 A, which represents the unmasking of which are accentuated and only slightly re- this d-spacing with the collapse of the kaolinite duced after heating for 2 hours at 550°C. Some structure. Patterns of heated shear zone speci- kaolinite lines which appear in the patterns of
TABLE 4. X-RAY DIFFRACTION D-SpAciN"G AND INTENSITY MEASUREMENTS FOR UNTREATED AND HEATED DICKITE Random orientation
Vcinlet filling clay from Lisbon Blackbird Copper Mine. San Juanito, Mexico Valley fault zone (58) Lisbon Valley, Utah Untreated Untreated Heated Heated dA Irel. dA I rel. dA Irel. elA I rcl. 7.19 100 7.19 100 7.19 100 7.19 100 4.458 37 4.458 21 4.458 24 4.458 35 4.372 46 4.372 24 4.350 31 4.372 40 4.267 17 4.267 22 4.267 39 4.138 44 4.148 21 4.148 29 3.948 11 3.966 10 3.983 18 3.966 10 3.863 12 3.897 1 3.799 17 3.815 j 18 3.783 20 3.588 89 3.574 100 3.581 100 3.588 80 3.464 11 3.437 18 3.477 30 3.424 15 3.264 3 3.241 10 3.108 4 3.129 5 3.129 1 10 3.006 7 3.076 J 10 3.076 5 2.929 5 2.561 15 2.561 11 2.561 14 2.561 15 2.536 10 2.526 12 2.533 10 2.506 23 2.496 18 2.493 19 2.499 10 2.428 17 2.409 14 2.409 10 2.389 15 2.383 15 2.383 13 2.383 15 2.324 42 2.341 30 2.336 24 2.341 20 2.252 3 2.209 6 2.179 3 2.194 5 2.189 6 2.164 5 2.092 3 2.074 3 1.975 12 1.991 13 1.987 11 1.983 10 1.935 5 1.939 6 1.939 6 1.929 6 1.912 5 1.897 6 1.897 5 1.893 5 1.860 4 1.842 5 1.836 6 1.792 6 1.789 10 1.785 6 1.805 10 ] Indicates broad peak
mens distinguish the dickite d-spacings, par- untreated specimens suggest it may be a vein ticularly the peaks neighboring the (002) line. constituent also, but more likely it represents Material was separated from the tiny white contamination scratched from the walls of the veinlets of the mineralized shear zone speci- veinlets. X-ray diffraction patterns of un- mens by prying particles from the fractures oriented, untreated, and heated samples of the with a needle under the binocular microscope. white vein-filling clay (Fig. 4; Specimens 52,
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UNTREATED
40 DEGREES 2& ANGSTROMS 3.5 10 17
Figure 4. X-ray diffraction patterns of dickite filling white veinlets of Lisbon Valley fault zone, samples 52, 58, and 54, Norlh Alice incline.
Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/76/4/423/3432262/i0016-7606-76-4-423.pdf by guest on 25 September 2021 Figure 1. Outcrop of highly silicified sandstone along Lisbon Valley fault, near Big Indian mine
Figure 2. Chalcedonic lens in North Alice mine, Lisbon Valley. The chalcedony is trav- ersed by veinlets filled with calcite. SILICA OCCURRENCES NEAR LISBON VALLEY FAULT, UTAH
JACOBS AND KERR, PLATE 1 Geological Society of America Bulletin, volume 76
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Figure 2. Fractured green clay from gouge zone of a small fault in Burro Canyon Forma- tion, North Alice workings, Lisbon Valley. Note white veinlets which are filled with dickite.
MINERALIZED GOUGE AND SHEAR ZONE SPECIMENS, LISBON VALLEY, UTAH JACOBS AND KERR, PLATE 2 Geological Society of America Bulletin, volume 76
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54, 58), together with d-spacings of North the walls and surrounds pyrite which fills the Alice dickite compared with dickite A.P.I. 15a center of the fracture. The relationship sug- from San Juanito, Chihuahua, Mexico (Table gests that vein-filling pyrite formed after 4; Specimen 58) furnish confirmation of the dickite. identity of dickite. Thin sections of fractured gouge zone clay Refractive indices of the white material fill- (PL 2, fig. 2) from a small fault in the Burro ing the veins are difficult to determine because Canyon Formation, 150 feet away from the of minute grain size and the orientation effect major shear zone, exhibit a yellow brown of the tabular clay mineral. The basal cleavage groundmass with high birefringence and a interfered with the determination of n0 until matted micaceous aggregate texture, consisting powdered glass was mixed with the specimens of kaolinite and illite with montmorillonite. to obtain random orientation of dickite flakes. Occasional tiny angular grains of feldspar and Optical determinations are essentially identical quartz appear in the groundmass along with with the indices for dickite from Xational Belle altered biotite remnants and irregular black mine, Red Mountain, Ouray, Colorado (Ross blebs of asphalt. The matrix is traversed by and Kerr, 1931) as follows: small dickite veinlets. Dickite from Burro Canyon Alteration Dickite from Lisbon Valley, Utah The matrix clay minerals in silicified Burro Ouray, Colorado (NA 58, Sodium Light) Canyon Sandstone are minor constituents be- n0'= 1.560 n« = 1.560 + .002 cause the formation is extensively silicified in np = 1.562 H., = 1.562 ± .002 the vicinity of the fault. The clean Burro nT = 1.566 nT = 1.566 + .002 Canyon Sandstone offered only a source of In addition, the fragments are generally color- silica to invading solutions, in contrast to the less, with low birefringence, and have extinc- clay-forming constituents found in Chinle tion angles between 15° and 20°. strata. Consequently, intensive silicification, Associated minerals. Several interesting oc- instead of clay mineral alteration, of the for- currences are associated with the alteration mation occurred. A minor amount of kaolinite clays of the Lisbon Valley fault zone. Lustrous occurs in strata near the shear zone, and X-ray black asphaltic material occurs in blebs up to reflections suggestive of alunite have been 2.5 cm across (PL 2, fig. 1). The X-ray diffrac- observed. tion pattern displays a broad, diffuse hump be- A number of Burro Canyon specimens have tween 10° and 25° 26, with a crest at about been examined in thin section. Burro Canyon 4.7 A, which is characteristic of indurated quartzite contains semirounded grains of quartz asphalt. Pyritc cubes are disseminated through- and occasional feldspar, fringed and cemented out the matrix and also fill veinlets. Jarosite with chalcedonic radial overgrowths. Chal- occurs in some specimens. cedomc radial overgrowths on grains with dis- Shear zone specimens in thin section (Fig. 5) tinct edges suggest that silicification occurred exhibit a light-brown groundmass with high as an additive process. Some grains are totally birefringence and a fine micaceous aggregate replaced by chalcedony with aggregate struc- texture under crossed nicols. The matted ture. Quartzites which appear less silicified in groundmass is largely kaolinite and mixed- hand specimens consist of semirounded grains layer illite-montmorillonite, and in places con- cemented by chalcedony with a salt and pepper tains quartz and feldspar grains, biotite altered texture, but lack border overgrowths around to kaolinite, veinlets filled by colorless clay the grains. Both show areas invaded by colorless with low birefringence identified as dickite, and kaolin clay with low birefringence. In sheared fine blebs of hardened asphalt. Some dctrital and altered sandstone, several crystal margins grains exhibit rims of opaque black asphaltic show destroyed and indistinct borders which material. Some feldspar grains exhibit thin blend with the chalcedony cement, suggesting outer rims of clay, whereas others are com- that a certain amount of metamorphism oc- pletely altered to kaolinite. Quartz grains show- curred, with solution of quartz grains from heat wavy extinction. Square cross sections of pyrite and pressure of faulting followed by recrystal- may be observed disseminated throughout the lization. A nearby conglomerate of subangular groundmass, which is traversed by numerous to subrounded quartz and feldspar grains is veinlets of pyrite and dickite. When the two cemented by chalcedony which exhibits fringes minerals fill the same vein, dickite occurs along of radial overgrowth. Brown jarosite with high
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birefringence appears in aggregates along grain with strongest clay peaks belonging to ka- boundaries and fractures of Burro Canyon olinite, along with mixed-layer clay. In certain samples. specimens, heating destroys the kaolinite pat- Silicification within the immediate vicinity terns and unmasks traces of chlorite, which of the fault zone is related to (1) additive yield low peaks at 13.58 A, 7.19 A, and 3.54 A. processes from active solutions in the fault zone, The underlying green-shale unit contains and (2) solution and rccrystallization from heat mixed-layer illite-montmonllonite. The un- and pressure of movement. This Silicification is treated X-ray pattern is dominated by a 10.77
K, I-M
5 mm
Figure 5. Thin section sketch of veinlet filled with pynte and dickite in shear zone (specimen NA 58). D = dickite, P = pyrite, K = kaolinite, A = asphalt, I-M = mixed-layer illite-montmorillonite. Ordinary light, 3.2 objective, 5 X ocular.
not the same as the thin (1-8 feet thick) A peak which spreads on glycolation to abroad quartzite unit at the top of the Burro Canyon, peak lying between 9.30 A and 11.62 A, and observed in localities where complete sections collapses on^ heating to a peak between 9.71 A of the formation have been preserved (Carter, and 10.16 A. Quartz is generally present and 1956, p. 113). The Silicification of the thin jarosite may be found. uppermost Burro Canyon Formation was In thin section, specimens from the siliceous caused by weathering conditions active before copper-bearing knob (PL 1, fig. 1) along the the overlying beds were deposited (Carter, access road close to Big Indian mine appear as 1956). coarse sandstone impregnated with silica. Rounded to subrounded quartz grains with dis- Big Indian Copper-Bearing Strata tinct edges are fringed with radial overgrowths The clay-mineral suite in the copper-bearing of chalcedony. Cretaceous strata of the Big Indian open pit along the fault is quite similar to the Chinle Blackbird Copper-Bearing Strata suite of the Lisbon Valley fault zone as exposed The clay material from the matrix of copper- along the North Alice incline. Most of the bearing sandstones and conglomerates from the copper-bearing sediments show X-ray patterns Blackbird workings (Fig. 1) consists of kaolin,
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illite, and 12.10 A mixed-layer illite-mont- temperature environments may exist but are morillonite. Glyeolation sharpens the 10 A infrequently found. Some reported occurrences illite peak and indicates that the mixed-layer should be reconsidered because crystal proper- clay consists largely of nonexpanded layers. ties of material called dickite appear to belong Heating collapses the mixed-layer clay to an tokaolinite. Boswell (1933) reports Tomkcieff's intense 10 A peak and reduces, but does not occurrence from clay-ironstone of Coal Measure eliminate, the reflections ot the kaolin member. age as dickite, although it was originally identi- When the white clay filling cavities of al- fied as kaolinite and described as having parallel tered detrital grains oi the conglomerate was extinction. Similarly, the alleged dickite re- selectively sampled and analyzed, the kaolin ported by Dunham and others (1949) as oc- was identified as dickite. The diflractogram re- curring with cellophane in the magnesium mains unchanged after heating the specimen limestone of Durham was identified from in- for two hours at 550°C and is comparable to distinct powder photographs with faint spotted the pattern of the A.P.I, dickite reference 15a lines. The photographs were described by Dun- (Table 4). ham as lacking well-defined high order lines Thin section study indicates that the clay that characterize powder patterns of dickite minerals are interstitial between detrital grains from Colorado and Anglesey (Ross and Kerr, and occur as partial or total alteration of feld- 1931). An occurrence of a Trigonocarpus fossil spar grains. Secondary chalcedony and aggre- fern fruit replaced by galena, sphalerite, and gates of green and blue oxidized copper min- pyrite, with dickite and kaolinite filling cracks erals are also prevalent. (Keller, 1947), also appears to merit reconsid- eration because X-ray patterns were described Significance of Dictate Occurrence as resembling both dickite and kaolinite. No As indicated by occurrences on record, the extinction angles greater than 5° were observed. presence of dickite suggests the action of hydro- Brindley and Robinson (1948), however, ex- thermal solutions, as lor example in Lcwistown, amined clays and shales from the Yorkshire Montana; San Juanito, Chihuahua, Mexico; Coal Measures and reported quartz, muscovite, and Ouray, Colorado, in association with pri- chlorite, anatase, and kaolinite and dickite in mary sulphides (A.P.I. Research Project 49, ironstone nodules. Honess and Williams (1935) 1951); and the island of Anglesey in Wales summarized the optical, chemical, and X-ray (Dick, 1888; Ross and Kerr, 1931). According data of dickite from two localities in coal mea- to Ross and Kerr (1931) dickite commonly sures in Pennsylvania. There the clay occurred occurs associated with metallic minerals. with transparent quartz and a small amount of Frankel (1949) reports dickite, of hydro- pyrite and "magnetic material." Authigenic thermal origin, in the Witwatersrand gold- dickite has been reported from Carboniferous bearing rocks. In the Daggafontein mine, sandstones from northern England and Wales dickite is found in gray-green clay-sized ma- and mid-Jurassic sandstones from northeast terial consisting of quartz and chloritic ma- Yorkshire (Smithson, 1954), and is thought to terial with small py rrhotite crystals and kidney- be caused by postdepositional changes depend- shaped particles of black organic material (spe- ent upon depth of burial. The heavy mineral cific gravity 1.27); in the Consolidated Main assemblage associated with the dickite is im- Reef mine, it occurs on quartz crystals and on poverished: garnet and feldspar are corroded; nodular pyritc. In the Rand Leases and Lang- authigenic anatase is observed; and quartz, laagte Estates, dickite adheres to aggregates of zircon, and tourmaline have authigenic out- small quartz crystals growing from the walls of growths. It may be that some dickite forms at vugs; the quartz contains veinlike growths of low temperatures under conditions that afford lustrous black organic material. Scattered in reorganization and reordering of the stacking the dickite aggregates, black organic matter sequence of kaolin layers (Personal communi- may be lound as well as minute crystals of cation, Dr. Richards Rowland). pyrite, pyrrhotite, and chalcopyrite. Whiteside Ross (1945) considers kaolinite as the most (1942) has described a suite of minerals from a stable of all the clay minerals. It forms under a vug in a quartz vein in the Kimberley series, wide range of conditions, but has a tendency which included quartz, chlorite, dickite, a to form in an acid environment, from humic hydrocarbon, galena, sphalerite, chalcopyrite, acids or oxidizing sulphides, and may also be pyrrhotite, and pyrite. the result of strong leaching action. Kaolinite Occurrences of dickite possibly from low- may form at low temperature or during min-
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eralization processes in the presence of warm bodies occur in veins and disseminated masses waters. Ross (1945, p. 182) states that ". . . in the lower part of the Mississippian Jackfork where hydrothermal processes are clearly indi- quartzitic sandstone. Dickite, with a 15° cated, dickitc, another of the kaolin minerals, extinction angle, occurs in quartz veins which has commonly formed rather than kaolinite." follow fractures and bedding planes. According Kerr (1955, p. 23) observes that dickite ". . . is to Sohlberg, (1933, p. 7), "... after the folding a less abundant clay mineral, and only in a few and faulting of the region, hydrothermal places such as San Juanito and Ouray have solutions rose along the fractures and fissures masses of any considerable size been found." of the Jackfork quartzitic sandstone, deposit- In a study of mineral associations of hydro- ing vein quartz, dickite, and cinnabar in the thermal alteration, Schwartz (1956) observes order named but with some local overlapping." that clay minerals form in the early stage of In western Arkansas, quartz deposits occur mineralization; argillation is the advancing in deformed Paleozoic shales and sandstones, front of the alteration. In his review of hy- exposed along the central belt of the Ouachita drothermal deposits, he mentions the occur- Mountains. Deposition of the quartz is con- rence of dickite: (1) at Cerro de Pasco, in the trolled by steeply dipping fractures. According most intense phase close to copper ore, with to Engcl (1946, p. 598), ". . . they are largely quartz, pyritc, kaolin, zunite, alumte, and cavity fillings, apparently deposited by rising, zoisite; (2) in Boulder County, Colorado, in attenuated, hydrothermal solutions, at re- the inner zone with sericite, hydrous mica, latively low temperatures and pressures." The quartz, and adularia; and (3) at Butte, Mon- rocks enclosing the quartz deposits show only tana, in a sericite zone with sericite, quartz, slight alteration or replacement. The minerals pyrite, and alunite. He notes that the sericite associated with the quartz include dickite and zone grades into kaolinite and then to a carbonaceous material, calcite, adularia, chlo- montmorillonite subzone. Schwartz (1956) rite, pyrite, sphalerite, galena, and chalcopy- observed that deposits at Castle Dome and rite. Dickitc is widely distributed as fine- Morenci, Arizona, have a phase involving grained aggregates in quartz-filled cavities and sericite, quartz, kaolinite, and pyrite. In a as vcmlets coating fissures in massive quartz. study of alteration accompanying disseminated Tarr and Keller (1936) describe dickite as- copper ores, Schwartz (1947) and Kerr and sociated with millerite, chalcopyrite, galena, others (1950) observe the occurrence of pyrite, and wurtzite in chert from Missouri. kaolinite, hydromica, dickite, and sericite in Allen (1936) observed dickite in a geode com- the highly altered porphyry in the Chino posed of layers of chalcedony and quartz, with deposit at Santa Rita, New Mexico. no sulphides associated. Both investigators In Bolivia, antimony deposits have a wide accept a hydrothermal origin for the mineral at distribution along the Andes in shatter zones localities far removed from proven igneous near the anticlines in Ordovician slates. Al- activity. though no outcrops of igneous rocks may be From the nature of observed dickite oc- observed nearby, stibnite, ferberite, pyrite, currences, its association with sulphides and gold, quartz, and dickite fill veins considered silicification and its formation in environments to be of hypabyssal-epithermal origin, the last marked by higher temperatures appear to be phase in the Bolivian tin mineralization recurrent. Its occurrence near thermal springs (Ahlfeld, 1952). Ahlfeld also reports nearby with hydrogen sulphide in Bolivia is significant evidence of thermal springs with H2S and in suggesting one facet of the chemical environ- alkali. ment favorable for its formation. Dickite considered to be hydrothermal in Several investigators have synthesized kaolin- origin has been found in cavities in a pre- ite and dickite in the laboratory. Investiga- cambrian crystalline limestone in southwestern tions prior to 1937 which yielded temperatures Finland (Pehrman, 1958). of hydrothermal mineral formation have been In Russia, the Kara-cheku massif consists reviewed by Morey and Ingerson (1937). mainly of secondary quartzites formed from Schwarz and Walcker (1925) synthesized prophyry tuffs by hot sulphuric waters. kaolinite from a silica-alumina gel, in which Dickite occurs (Nakovnik, 1940) in the altered Al/Si was 1/6, as the ratio in potassium porphyry as a massive bed and also disseminated feldspar. After the pH was varied from 4.10 to in quartzite with alunite. 9.25, it was found the pH 4.5-5.2 provided the In Pike Countv, Arkansas, cinnabar ore most favorable range. Ewell and Insley (1935)
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synthesized kaolinitc at 310°C from AUCV veinlets of dickite traverse rocks of the highly SiOa gel with water in a bomb, and dickite fractured and mineralized gouge zone. Massive from Al2O3-SiO2 gels between 350°C and pyrite accompanies dickite in veinlets which 365°C. Using silica gel and alumina gel in a cut through a matrix of mixed-layer ilhte- bomb, Noll (1935) synthesized kaolinite be- montmorilionite and kaolinite. Tiny pyrite tween temperatures of 250°-400°C and pres- cubes, possibly a different generation, arc dis- sures of 41-300 atm. tributed through the clay matrix. Jarosite, Norton (1939) exposed feldspar and alu- which is also present, may be secondary after minum silicate minerals to CCVcharged per- pyrite, but it may also result from late hy- colating water under high pressures and tem- drothermal activity as a vein mineral (Kerr peratures in a reaction chamber. He observed and others, 1957, p. 88), as noted in the the greatest reaction rate at 300°C with a uranium deposits at Marysvale, Utah, and the maximum CO2 pressure and produced kaolin- hot spring tungsten deposit at Golconda, itc, bcidellite, sericitc, pyrophyllite, and Nevada (Kerr, 1940, p. 1372). Dickite is gibbsitc. Between 250° and 350°C he con- found in a gouge zone of a smaller fault 150 verted spodumene to kaolinitc and anorthite feet in the hanging wall. It also replaces to pyrophyllite. Using the same materials under dctntal feldspar grains in the sandstones and higher CO2 pressures, Norton (1941) produced conglomerates of the Blackbird copper work- kaolinite and dickite between 250° and 300°C; ings. As indicated by occurrences of dickite on and kaolinite at 325°C as pressure varied record (Dick, 1888;'Frankel, 1949; Whireside, between 125 and 970 atm. 1946; Schwartz, 1947; 1956; Ahlfeld, 1952; In hydrothermal experiments using kaolin Pchrman, 1958; Nakovnik, 1940; Sohlberg, minerals, halloysitc, pyrophyllite, and alumina- 1933; Engel, 1946; Tarr and Keller, 1936; silica gels at varied temperatures and pressures, Allen, 1936), irs occurrence generally suggests Roy and Osborn (1954) obtained kaolinite, the action of hydrothermal solutions. Hard- dickite, nacrite, pyrophyllite, and Al-mont- ened asphalt occurs as blebs in the matrix and morillonite. An upper stability temperature as rims around detrital grains. The hardened of 405°C was determined lor kaolinite oi asphalt and its mineral associates that occur on hydrothermal origin and for nacrite and dickite the San Rafael Swell (Abdel Gawad and Kerr, which commonly have a hydrothermal origin. 1961) become indurated by heat at tempera- In summary, dickite has been synthesized tures from 250° to 300°C, which suggests hydrothermally between temperatures of 250°C temperatures compatible with thermal activity. and 365°C from materials which include kaolin Alteration in the Burro Canyon porous minerals, alumina-silica gels, and aluminum sandstone occurring in the hanging wall has silicates. An upper stability temperature of produced extensive silicifieation, which has 405°C has been observed. Such laboratory changed the sandstone into quartzite lor 50 syntheses shed much light on the formation of or more feet away from the fault. Silicifieation dickite in nature. may also be observed in the surface areas along fractures, as massive impregnations of coarse SUMMARY AND CONCLUSIONS sandstone or conglomerate, and as red chal- Bleaching accompanying argillic alteration cedonic lenses such as in the North Alice mine. produces changes in Chinlc strata from deep An epigenctic origin has been attributed to the red brown to gray green and gray white close red chalcedony (Weir and others, 1956, p. 58) to the Lisbon Valley vault. Kaolinization is found in Cutler and Chinlc strata and also on most intense within and close to the fault zone, the erosional surface between them. extending intermittently 50 to 300 ieet away. Copper minerals have been deposited in Mixed-layer ilhte-montmonllonitc with a prom- scattered localities along the Lisbon Valley inent 11-15.5 A basal spacing accompanies fault, for the most part in the Cretaceous kaolinite. Study of many Chinlc specimens Dakota Sandstone, but also in Permian, from Lisbon Valley indicates that the forma- Triassic, and Jurassic strata in Lisbon Valley tion normally contains ilhte, chlorite, mont- and in Tertiary brecciated igneous rock in the morillonite, and mixed-layer illite-montmoril- nearby La Sal Mountains. The mineral as- lomte, but near the Lisbon Valley fault zone it semblage includes sulphides such as chalcocitc, is predominantly kaolinitic. digenite, and bornitc, as well as abundant Along the shear zone of the fault, argillic oxidized minerals such as cuprite, malachite, alteration is most intense. Mvriads of fine chrysocola, and azurite. Covellite, chalcopy-
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rite, tenorite, and native copper are reported thermal solutions. Copper-rich solutions miner- to be widespread in trace amounts (Weir and alized the porous Dakota Sandstone and the Puffett, 1960, p. 137). "Because the copper numerous subsidiary fractures associated with deposits are mainly in fractured rock near the major fault zone. Carbonate-bearing solu- faults over a wide stratigraphic range, and tions filled fractures in copper sulphides with include a deposit in brecciated igneous rock, calcite. they are considered low-temperature hypogene The uranium-bearing Moss Back Member deposits" (Weir and Puffett, 1959, "p. 10). follows an arcuate pattern around the upthrown Hunt (1958, p. 338, 355) ascribed a hydro- anticlinal limb, but at each end oi the arc thermal origin to the copper deposits in the uranium-rich ore zones are cut sharply by the igneous rocks of the La Sal Mountains, as Gott Lisbon Valley fault. These Chinle strata pro- and Erickson (1952) have lor the Lisbon Valley vided an environment which sustained reducing copper deposits. conditions necessary for uranium precipitation. The clay-mineral assemblage, indurated hy- According to Weir and Puffett (1958, p. 25; drocarbons, bleaching, silicification, and per- 1959, p. 10; 1960, p. 146), certain similarities vasive copper mineralization along the Lisbon between the uranium-vanadium and copper Valley fault indicate that heated mineralizing deposits, such as the wide stratigraphic range solutions were active. Probably different gen- of both, their occurrence replacing carbon- erations of solutions occurred. Solutions of aceous debris, and common occurrence in many acidic nature, possibly enriched in hydrogen deposits, suggest deposition from solutions of sulphide, bleached the wall rock by reducing similar origin as those that deposited copper in ferric oxide pigment and precipitated metallic igneous rocks. Evidence of the action of thermal sulphides. Intense development of kaolinite mineralizing solutions rising along the Lisbon and dickite in the shear zone indicates the Valley fault zone makes the source of uranyl effectiveness of migrating solutions in altering ions for these deposits possibly hypogene. The the country rock. Silicification suggests higher passage of solutions to the Chinle most likely pH values at times. Indurated asphalt suggests occurred by way of subsidiary fractures, joint that hydrocarbons, brine, and natural gas, planes, and the porous Permian sugar sand possibly released from underlying petroliferous beds, and spread out from fractures caused by Paleozoic strata by Cretaceous folding and major faulting. faulting, moved up the same fractures as the
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MANUSCRIPT RECEIVED BY THE SOCIETY MAY 13, 1963 REVISED MANUSCRIPT RECEIVED AUGUST 7, 1964
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