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Title: Paragenesis and conditions of formation of ore minerals from metalliferous breccia pipes, N. Arizona

Abstract

Ore deposits within N. Arizona breccia pipes are currently being exploited for U, but at various times during the past century Cu, Pb, Zn, and Ag were mined. These pipes formed as solution-collapses within the Mississippian Redwall Ls and stopped upward through overlying strata. The principal ore minerals are: uraninite, chalcopyrite, chalcocite, tennantite-tetrahedrite, galena, sphalerite, millerite, gersdorffite, siegenite, and molybdenite. Common gangue minerals are marcasite, pyrite, barite, dolomite, calcite and quartz. Marcasite and pyrite appear to have formed prior to the ore minerals, followed closely by chalcopyrite. The Ni and Co phases also appear to be early: gersdorffite crystals are rimmed by later galena. Tennantite-tetrahedrite formed later than both galena and sphalerite; uraninite, the latest ore mineral, consisting fills interstices. Primary fluid inclusions in dolomite, quartz, and sphalerite show filling temperatures from 80 to 145/degree/C and high salinities, averaging 15 wt% NaCl (eq). Secondary inclusions in sphalerite have consistently higher filling temperatures from 105 to 173/degree/C, but similar salinities. Rock-Eval pyrolysis of pyrobitumen yields little or no volatile hydrocarbons (S/sub 1/=0-0.2 mg/gm), but large amounts of pyrolytic hydrocarbons (S/sub 2/=105-216 mg/gm). Temperatures of maximum pyrolytic yield are relatively low (424-430/degree/C), suggesting temperatures did not exceed 150/degree/C following pyrobitumen emplacement. Exceptmore » for uraninite, the breccia pipes are similar to Mississippi Valley-type (MVT) deposits in mineralogy, fluid-inclusion filling temperatures and salinities, and associated organic material. Because MVT deposits do not host U minerals, a possible two-stage mineralization history of the pipes is suggested, the first by a MVT brine and perhaps a second forming the uraninite.« less

Authors:
;
Publication Date:
Research Org.:
Geological Survey, Denver, CO (USA)
OSTI Identifier:
6005226
Report Number(s):
CONF-8510489-
Journal ID: CODEN: GAAPB
Resource Type:
Conference
Resource Relation:
Journal Name: Geol. Soc. Am., Abstr. Programs; (United States); Journal Volume: 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28-31 Oct 1985
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 58 GEOSCIENCES; ARIZONA; URANIUM ORES; MINERALIZATION; MINERALOGY; BARITE; BRINES; CHALCOPYRITE; DOLOMITE; GALENA; GEOLOGIC HISTORY; GEOTHERMOMETRY; HYDROCARBONS; INCLUSIONS; LIMESTONE; MISSISSIPPIAN PERIOD; PARAGENESIS; PYRITE; QUARTZ; SPHALERITE; URANINITES; ALKALINE EARTH METAL COMPOUNDS; BARIUM COMPOUNDS; BARIUM SULFATES; CALCIUM CARBONATES; CALCIUM COMPOUNDS; CARBON COMPOUNDS; CARBONATE MINERALS; CARBONATE ROCKS; CARBONATES; CHALCOGENIDES; COPPER COMPOUNDS; COPPER SULFIDES; FEDERAL REGION IX; GEOLOGIC AGES; IRON COMPOUNDS; IRON SULFIDES; LEAD COMPOUNDS; LEAD SULFIDES; MAGNESIUM CARBONATES; MAGNESIUM COMPOUNDS; MATERIALS; MINERALS; NORTH AMERICA; ORES; ORGANIC COMPOUNDS; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; PALEOZOIC ERA; RADIOACTIVE MATERIALS; RADIOACTIVE MINERALS; ROCKS; SEDIMENTARY ROCKS; SILICON COMPOUNDS; SILICON OXIDES; SULFATE MINERALS; SULFATES; SULFIDE MINERALS; SULFIDES; SULFUR COMPOUNDS; TRANSITION ELEMENT COMPOUNDS; URANIUM MINERALS; USA 050100* -- Nuclear Fuels-- Reserves, Exploration, & Mining; 580300 -- Mineralogy, Petrology, & Rock Mechanics-- (-1989)

Citation Formats

Wenrich, K.J., and Pratt, L.M. Paragenesis and conditions of formation of ore minerals from metalliferous breccia pipes, N. Arizona. United States: N. p., 1985. Web.
Wenrich, K.J., & Pratt, L.M. Paragenesis and conditions of formation of ore minerals from metalliferous breccia pipes, N. Arizona. United States.
Wenrich, K.J., and Pratt, L.M. 1985. "Paragenesis and conditions of formation of ore minerals from metalliferous breccia pipes, N. Arizona". United States. doi:.
@article{osti_6005226,
title = {Paragenesis and conditions of formation of ore minerals from metalliferous breccia pipes, N. Arizona},
author = {Wenrich, K.J. and Pratt, L.M.},
abstractNote = {Ore deposits within N. Arizona breccia pipes are currently being exploited for U, but at various times during the past century Cu, Pb, Zn, and Ag were mined. These pipes formed as solution-collapses within the Mississippian Redwall Ls and stopped upward through overlying strata. The principal ore minerals are: uraninite, chalcopyrite, chalcocite, tennantite-tetrahedrite, galena, sphalerite, millerite, gersdorffite, siegenite, and molybdenite. Common gangue minerals are marcasite, pyrite, barite, dolomite, calcite and quartz. Marcasite and pyrite appear to have formed prior to the ore minerals, followed closely by chalcopyrite. The Ni and Co phases also appear to be early: gersdorffite crystals are rimmed by later galena. Tennantite-tetrahedrite formed later than both galena and sphalerite; uraninite, the latest ore mineral, consisting fills interstices. Primary fluid inclusions in dolomite, quartz, and sphalerite show filling temperatures from 80 to 145/degree/C and high salinities, averaging 15 wt% NaCl (eq). Secondary inclusions in sphalerite have consistently higher filling temperatures from 105 to 173/degree/C, but similar salinities. Rock-Eval pyrolysis of pyrobitumen yields little or no volatile hydrocarbons (S/sub 1/=0-0.2 mg/gm), but large amounts of pyrolytic hydrocarbons (S/sub 2/=105-216 mg/gm). Temperatures of maximum pyrolytic yield are relatively low (424-430/degree/C), suggesting temperatures did not exceed 150/degree/C following pyrobitumen emplacement. Except for uraninite, the breccia pipes are similar to Mississippi Valley-type (MVT) deposits in mineralogy, fluid-inclusion filling temperatures and salinities, and associated organic material. Because MVT deposits do not host U minerals, a possible two-stage mineralization history of the pipes is suggested, the first by a MVT brine and perhaps a second forming the uraninite.},
doi = {},
journal = {Geol. Soc. Am., Abstr. Programs; (United States)},
number = ,
volume = 17,
place = {United States},
year = 1985,
month = 1
}

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  • The price of uranium is currently the lowest in more than a decade. The only type of uranium deposit that is economically viable in the depressed uranium market is such high-grade ore as the unconformity type found in Canada and Australia. Exploration for uranium-bearing breccia pipes in northwestern Arizona by both domestic and foreign companies is currently active because of the relatively high-grade ore they contain and their tendency to be polymetallic. In the US, uranium-mineralized breccia pipes are one of the few deposits that can compete in the current market. A stepwise discriminant analysis was performed on spectral datamore » acquired from the field, laboratory, and Landsat thematic mapper (TM). The principal objectives were (1) to investigate the fundamental differences in the spectral properties of outcrops on the surface of breccia pipes and the background, (2) to choose TM bandpasses that were statistically optimum for distinguishing between breccia pipes and the background, and (3) to compare the results of the field, laboratory, and TM digital data which were acquired by different instruments having different spatial and spectral resolutions.« less
  • An extensive suite of Ni-Co-Fe-Cu sulfides and arsenides lies within the matrix of solution-collapse breccias buried deep within the plateaus of the Grand Canyon region. Ceilings over large caverns in the Redwall collapsed, brecciating the overlying sandstone and forming cylindrical breccia pipes up to 300 ft in diameter that extend vertically as much as 3,000 ft. These highly permeable breccias served as a host for the precipitation of a suite of over 100 minerals, including uraninite, sphalerite, galena and various copper phases, in addition to the Ni-Co-bearing-phase discussed here. Intricately zoned crystals of small (<1 mm), euhedral Ni-Co-Fe-As-S minerals weremore » the first to form during the second major episode of mineralization in these pipes. Several of these phases replace minerals, such as barite and anhydrite, from the first episode. Extensive microprobe work has been done on samples from two breccia pipe mines, the Hack 2 and Orphan, which are about 50 miles apart. Mineral compositions are similar except that no copper is found in the Ni-Co-Fe phases from the Hack 2 mine, while pyrites containing 1 wt % Cu are common from the Orphan, which was mined for copper. In some of these pyrites', Cu is dominant and the mineral is actually villamaninite. Pyrites from both mines characteristically contain 0.5 to 3 wt % As. Metal contents in zones pyrite-bravoite-vaesite (M[sub 1]S[sub 2]) crystals at the Hack 2 mine range from Fe[sub 1] to Fe[sub .12], Ni[sub 0] to Ni[sub .86], and Co[sub 0] to Co[sub .10]. The metal content for polydymite-siegenite-violarite averages about (Ni[sub 2.33]Co[sub .39]Fe[sub .23])(S[sub 3.9]As[sub .1]). Orphan mine pyrite-bravoite-vaesite-villamaninite ranges in composition from pure FeS[sub 2] to (Ni[sub .6]Fe[sub .21]Co[sub .17])S[sub 2], and (Cu[sub .46]Ni[sub .27]Fe[sub .21]Co[sub .13])S[sub 2]. Of all the sulfides or arsenides found in these breccia pipes, only nickeline consistently occurs as the pure end member.« less
  • Thousands of solution-collapse breccia pipes may crop out in the canyons and on the plateaus of northern Arizona, and more than 80 contain uranium or copper mineralized rock; however, their small size and limited rock outcrop make them difficult to locate. Recognition of the pipes on the plateaus is particularly important because mining access to the plateaus is far easier than to the canyons. Several reconnaissance geochemical methods have been tested to help locate suspected and mineralized breccia pipes. (1) A hydrogeochemical survey conducted on the 1500 mi/sup 2/ (4000 km/sup 2/) Hualapai Indian Reservation appears to yield anomalous valuesmore » downstream from regions, such as Mohawk Canyon, where clusters of mineralized pipes occur. Pigeon Spring, east of the Pigeon mine, also had anomalous uranium (44 ppb). (2) A stream-sediment survey was not made on the Hualapai Reservation because the dilution factor that results from the large volume of country rock, compared to that of mineralized rock, swamps out any low-level geochemical signature contributed to streams by rock or soil overlying breccia pipes. Several types of detailed geochemical and geophysical surveys, made over individual collapse features located through examination of aerial photographs and later field mapping, have generally been successful at delineating collapse features from the surrounding host rock: (1) rock geochemistry commonly shows Ag, As, Ba, Cu, Pb, Se, and/or Zn enrichments of from 3 to 100 times background levels over mineralized breccia pipes; (2) soil surveys appear to have the greatest exploration potential of the geochemical methods (e.g., samples collected from the centers of several collapse features show consistently twice the background value for a number of elements);« less
  • The development of caves within the Mississippian Redwall Limestone, accompanied by later upward stoping of overlying Paleozoic and Triassic rock, resulted in the formation of breccia pipes. Despite the depressed uranium market, some of these pipes are presently being mined for uranium. No brecciated rock within pipes has been observed above its normal stratigraphic position, nor is any volcanic rock associated in space or time with these pipes. Mineralized rock transects any strata from the Redwall Limestone to the Triassic Chinle Formation. Over 400 collapse structures, believed to represent breccia pipes (many with exposed breccia), have been mapped. Those withmore » gamma radiation exceeding 2.5 times background (57 pipes) have been sampled (155 samples). Of these oxidized surface samples collected solely on the basis of radioactivity, 30% have Ag exceeding 10 ppm, some with up to 1150 ppm. Two samples of brecciated, oxidized sandstone with radioactivity exceeding 20 and 40 times background from this adit, and another sample of hematite-, malachite-, and chalcocite-impregnated sandstone from a higher level adit contained high concentrations of Au, Hg, Cd, and W, along with many elements commonly anomalous in mineralized breccia pipes from northern Arizona: Ag, As, Co, Cu, Mo, Ni, and Pb. The potential for economic recovery from breccia pipes of elements other than U, such as Ag, Au, Co, and Ni, should not be ignored as their concentrations are even more enhanced in unoxidized samples.« less
  • During the 1950s and 1960s, the uranium deposits in breccia pipes of the Grand Canyon region were regarded as geologic curiosities. Today this area is the site of numerous exploration projects for ore-bearing pipes. The classic example of the older mines is the Orphan Lode, a patented claim within Grand Canyon National Park. Between 1956 and 1969, this deposit produced 4.26 million lb U/sub 3/O/sub 8/. Exploration since the mid-1970s has developed numerous new deposits in the Grand Canyon region. The Hack 1, 2, and 3, Pigeon, Kanab North, Canyon, and Pinenut deposits are, or will be, mined. The pipesmore » are circular and originated by dissolution of the Mississippian Redwall Limestone and collapse of the overlying strata. Uraninite ore occurs in both the pipe fill and in association with the peripheral shear zone. The principal host rocks are the Coconino Sandstone, Hermit Shale, and Esplanade Sandstone. Although small (3 to 5 million lb U/sub 3/O/sub 8/), the high grade (60 to 70% U/sub 3/O/sub 8/) of the deposits makes the pipes attractive exploration targets.« less