Field Trip Report - Society of Economic Geologists

 Society of Economic Geologists University of Arizona Student Chapter Copper, Silver, and Gold in California Edited by Jennifer Dabbs May 23-­‐June 1, 2015 The information contained in the report is for information purposes only. The information contained within the report may be changed or updated from time to time without notice. The authors of this report have taken all reasonable care in producing and publishing information contained in this report. Material in this report may contain technical or other inaccuracies, omissions, or typographical errors, for which the Society of Economic Geology assumes no responsibility. In consideration for using this material, the reader agrees to hold the Society and its affiliates harmless against any claims for damages or costs or any loss of any kind arising out of the access to or use of this report or any information contained in or obtained through this report. Technical information contained in this report is for personal use only. Any reliance on the information contained in these reports by any third party shall be entirely at their own risk. Cover image from: Department of Conservation State of California Geotour Website http://www.consrv.ca.gov/cgs/geotour/Pages/Index.aspx#sierra%20nevada
Acknowledgments The University of Arizona SEG student chapter would like to thank the following organizations and individuals for making this trip possible: Lowell Institute for Mineral Resources Society of Economic Geologists Data Metallogenica AMIRA International Mining Foundation of the Southwest Sarah and Don Baxter Robert Wetzel Norman Lamb Participants Participants Affiliations Jennifer Dabbs University of Arizona Jason Mizer University of Arizona Daniel Favorito University of Arizona Matthew Wetzel Sean O’Neal University of Arizona, Freeport-­‐McMoRan University of Arizona, Bronco Creek Exploration From left to right: Sean O’Neal, Daniel Favorito, Jennifer Dabbs, Jason Mizer, Matthew Wetzel, Cerro Gordo Mining District, California
Itinerary for University of Arizona SEG Student Chapter Field Trip Route for the 2015 UA SEG Field Trip to California: Moonlight Lights Creek District (Plumas
Copper Belt), McLaughlin Mine (Knoxville Mining District), Cerro Gordo Mining District, and
Bullfrog Mining Distirct (Nevada)
Sunday May 24, 2015 • Depart from Reno, NV • Tour Mt. Lassen Volcanic Park, CA • Camp at Goldstripe Mine, Plumas Copper Belt, CA Monday May 25, 2015 • Tour Goldstripe Mine, Lode Gold Deposit, CA • Visit the Moonlight Deposit, Plumas Copper Belt, CA • Tour Superior Mine, Plumas Copper Belt, CA • Camp near Engels Mine, Plumas Copper Belt, CA Tuesday May 26, 2015 • Tour Engels Mine, Plumas Copper Belt, CA • Camp at Cloverdale KOA Wednesday May 27, 2015 • Visit Knoxville Mining District, CA • Visit McLaughlin Mine area, CA • Camp at Cloverdale KOA Thursday May 28, 2015 • Visit Shell Beach, Sonoma Coast (Eclogites), CA • Visit Muir Woods National Monument, CA • Camp at Mariposa KOA Friday May 29, 2015 • Tour Yosemite National Park, CA • Stay at Bunk House in Cerro Gordo Ghost Town Saturday May 30, 2015 • Look at Cerro Gordo Mining District Core • Tour various prospecting pits, Cerro Gordo Mining District, CA • Tour Ignacio Mine, Cerro Gordo Mining District, CA • Tour Morning Star Mine, Cerro Gordo Mining District, CA • Stay at Bunk House in Cerro Gordo Ghost Town Sunday May 31, 2015 • Tour Estella Tunnel, Cerro Gordo Mining District, CA • Tour Death Valley National Park, CA • Visit Bullfrog Mining District, Nye County, NV • Stay in Las Vegas, NV Monday June 1, 2015 • Depart from Las Vegas, NV • Arrive in Tucson, AZ LIST OF VISITED MINE SITE COORDINATES Site District Latitude Longitude Gold Stripe Mine Plumas Copper Belt 40°10'0.25"N 121° 3'22.94"W Moonlight Deposit Plumas Copper Belt 40°13'13.07"N 120°48'9.29"W Superior Mine Plumas Copper Belt 40°12'10.57"N 120°46'28.01"W Red Elephant Deposit Knoxville Mining District 38°50'4.37"N 122°24'11.82"W Ignacio Mine Cerro Gordo Mining District 36°32'0.54"N 117°48'8.27"W Wheelbarrow Prospect Cerro Gordo Mining District 36°31'55.90"N 117°48'26.05"W Cerro Gordo Ghost Town Cerro Gordo Mining District 36°32'17.49"N 117°47'44.35"W Estelle Tunnel Cerro Gordo Mining District 36°31'15.31"N 117°48'54.26"W Morning Star Mine Cerro Gordo Mining District 36°31'28.81"N 117°47'43.38"W May 24 – May 26, 2015 MOONLIGHT-­‐LIGHTS CREEK DISTRICT PLUMAS COPPER BELT, CALIFORNIA Contributed by: Matthew Wetzel Sources: Graton, L.C., and McLaughlin, D.H., 1917, Ore Deposition and Enrichment at Engels, California: Economic Geology, v. 12, pp. 1-­‐38. Putman, G., 1975, Base Metal Distribution in Granitic Rocks. II: Three-­‐Dimensional Variation in the Lights Creek Stock, California: Economic Geology, v. 70, pp. 1125-­‐1241. Stephens, A., 2011, Mineralogy and Geochemistry of Copper Deposits of the Lights Creek Stock, California: An Assessment of Porphyry Versus Iron-­‐Oxide-­‐
Copper-­‐Origin: Unpublished Master’s Thesis, Oregon State University, pp. 1-­‐
145. Storey, L., 1978, Geology and Mineralization of the Lights Creek Stock, Plumas County, California: Arizona Geological Society Digest, v. 11, pp. 49-­‐58. Tollman, C.F., 1917, Response: Ore Deposition and Enrichment at Engels, California: Economic Geology, v. 12, pp. 379-­‐386. Wetzel, R., 2009, Report on the Moonlight Project, CA: Unpublished company report, pp. 1-­‐22 Field Trip Route: Geologic Background: The Moonlight-­‐Lights Creek district in the Sierra Nevada physiographic province is found within the Plumas Copper Belt, California, approximately 113km NNW of Reno, NV. According to Storey (1978), the region is influenced by basin and range faulting and is located on the northern portion of the Walker Lane structural liniment. The Lights Creek composite intrusion is made up of Late Jurassic-­‐ Early Miocene gabbro, granodiorite, quartz monzonite intrusions as well as post-­‐
mineralization, coarse-­‐grained granite. There are NNW striking, SW dipping Jurassic basaltic-­‐andesite to andesite flows exhibiting greenschist facies metamorphism that make up a roof pendant exposed in the Moonlight South portion of the district. The total measured thickness of the meta-­‐volcanic package has a maximum thickness of 1.5km. Bornite-­‐chalcopyrite-­‐chlorite-­‐hematite-­‐magnetite-­‐tourmaline mineralization cuts through portions of the roof pendant, as evident at the Ruby Mine, Trask and Coffer Mine, and other unnamed workings and vein outcrops throughout the Moonlight South area. This style of mineralization commonly represents the upper levels of the mineralization. Mineralization: Mining began at the Superior and Lights Creek deposits in 1890s but the main period of mining was from 1916-­‐1930, producing roughly 161.5 Mlbs of Cu Granodiorite with glassy limonite after chalcopyrite and copper-­‐
oxides after bornite, Engels Mine, Moonlight-­‐Lights Creek District, Plumas Copper Belt, California. Photo by J. Dabbs, 2015. with an average recovery grade of 1.79%Cu. The Moonlight Valley deposit, defined by Placer Amex Inc. in the 1990s, indicates potential mineralization at a 0.2% cutoff grade of 250Mt of Cu @ 0.35%, while the Superior deposit still contains approximately 100Mt @ 0.33% Cu. High grade areas commonly occur near the contact of the Lights Creek stock and the surrounding metavolcanics. Additional high-­‐grade mineralization is associated with the earlier mafic intrusives at the Engels Mine and shows a relationship to the zone of silicification or hornfelsing that has advanced outward from the Lights Creek stock. Copper deposition has largely occurred behind this silicification front within the intrusive at Moonlight and Superior. Copper deposition has also been noted in Tourmaline vein surface with minor copper-­‐oxide, Superior Mine, Moonlight-­‐
Lights Creek District, Plumas Copper Belt, California. Photo by J. Dabbs, 2015.
the zone of biotite granite dikes with abundant tourmaline. These dikes are interpreted to be late stage differentiates of the Lights Creek stock. Mineralized diabase dikes in the Lights Creek stock have been observed at the Superior deposit, raising the question of how long after the crystallization of the quartz monzonite some of the mineralization took place. Storey (1978) described the Moonlight-­‐Lights Creek District as an atypical porphyry-­‐type deposit while Stevens (2011) suggested the district more closely resembles an IOCG-­‐type deposit. More study is needed before a more complete genetic model can be developed for the Moonlight-­‐ Lights Creek Deposit. Accessibility: Much of the Moonlight-­‐
Lights Creek District is on National Forest Service Land and is therefore accessible to the public by unpaved road. Four-­‐wheel drive is suggested. The Superior Mine and Engel Mine are private property owned by the California-­‐
Engels Mining Company. The California-­‐Engels Mining Company must grant permission for access. For more information, contact Norman Lamb. Copper-­‐oxide in underground tunnel, Superior Mine, Moonlight-­‐Lights Creek District, Plumas Copper Belt, California. Photo by S. O’Neal, 2015.
May 26, 2015 MCLAUGHLIN MINE, KNOXVILLE MINING DISTRICT NAPA COUNTY, CALIFORNIA Contributed by: Jason Mizer and Jennifer Dabbs Sources: http://westernmininghistory.com/mine_detail/10310645 Peters, K.E., 1991, Gold-­‐Bearing hot spring systems of the Northern Coast Ranges, California: Economic Geology, v. 86, pp. 1519-­‐1528. Sherlock, R.L. and Lehrman, N.J., 1995, Occurrences of dendritic gold at the McLaughlin Mine hot-­‐spring gold deposit: Mineralium Deposita, v. 30, p. 323-­‐ 327. Field Trip Route: Modified from Peters (1991), Knoxville and Sulfur Creek mining districts with field trip route overlay. Geologic Background: The McLaughlin Mine (formerly Manhattan Mine) is located 115 km north of San Francisco in the Northern Coast Ranges of California in the Knoxville Mining District. The epithermal deposits of the Knoxville Mining District and nearby Sulfur Creek Mining District occur adjacent to the fault boundary between the Coast Range Ophiolite Sequence and the Great Valley Sequence. The Sulfur Creek Valley contains modern hot springs sourced from Great Valley sedimentary rocks, and isotopic evidence suggests that similar fluids were involved in the formation of the McLaughlin deposit. The McLaughlin deposit is a world-­‐class gold orebody. The epithermal system that created the deposit is associated with the Clear Lake Volcanic Field, which is the most recent of a NNW-­‐trending chain of Neogene-­‐Holocene volcanic fields. The two pits mined of the McLaughlin deposit follow the NNW trend of the Stony Creek Fault, which thrusts Great Valley Knoxville Formation mudstones and conglomerates over serpentinized ophiolite mélange rocks. The NNW striking fault dips at approximately 40 degrees to the northeast. At approximately 2.2 Ma, andesitic dikes intruded the Stony Creek thrust fault, and ore deposition occurred as recently as 750 ka. Mineralization: When the McLaughlin deposit was discovered, it had an intact cap of siliceous sinter. The terraces of siliceous sinter delineate the Pleistocene paleosurface associated with the formation of the deposit. Mineralization occurs in sheeted bodies and stockwork veins which are roughly 1cm thick. Most commonly, the veins are chalcedony and quartz, although Quartz and chalcedony veins in the Knoxville Mining District, California. The dark coloration is indicative of hydrocarbon residue. Photo by J. Dabbs, 2015. carbonate minerals occur in some veins. Due to the rapid cooling rates associated with hot springs-­‐type epithermal systems, mineralization is typically fine-­‐grained. Thus, the majority of the gold in the McLaughlin deposit is microscopic. As Homestake developed the McLaughlin Mine, they found several larger gold specimens. Dendritic gold commonly accompanies pyrite, arsenopyrite, and silver sulfosalts such as pyrargryrite and myargyrite. The most abundant occurrence of gold is with silver in electrum, and the average Ag/Au ratio is 3.5 by weight. This ratio varies with depth, however, ranging from less than 1:1 at the surface to grater than 30:1 at depth. Fluid inclusion analysis by Peters (1991) shows that hydrocarbons were present in the ore-­‐
forming fluids. Additionally, the gold ore is enriched in Hg, Sb, As, and Tl. Surface soil in the surrounding district contains cinnabar and free Dendritic gold with pyrargryite fringe in quartz/chalcedony in exploration core, North Pit, McLaughlin Mine, CA. Darker coloration in the quartz is indicative of hydrocarbon residue. Photo by D. Enderlin. gold. Mining History: The McLaughlin Mine is located on the site of the former Manhattan Mine, which was mined for Mercury from the 1860s until 1978. The total ore mined from the north and south pits of the McLaughlin Mine is roughly 38 Mt at 0.110 ounces Au/ton, with a total of just under 4 million ounces produced. Accessibility: The Knoxville Recreation Area is managed by the BLM, and is therefore open to the public. Four-­‐wheel drive is recommended. Barrick Mining Corporation, who must grant permission for access, privately holds the McLaughlin Mine. May 29 – May 31, 2015 CERRO GORDO MINING DISTRICT INYO COUNTY, CALIFORNIA Contributed by: Daniel Favorito and Jennifer Dabbs Sources: http://www.mindat.org/loc-­‐27431.html Merriam, C.W., 1963, Geology of the Cerro Gordo Mining District Inyo County, California: Geological Survey Professional Paper 408 Stone, P., et al., 2004, Geologic Map of the Cerro Gordo Peak 7.5'Quadrangle, Inyo County, California. USGS Scientific Investigations Map, No. 2851. Field Trip Route: Geologic map of the Inyo Mountain area, from Stone et. al. (2004). 117o45'
118o00'
118o15'
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117o30'
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CERRO
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10 KILOMETERS
Late Cenozoic
normal fault—Dotted
where concealed. Bar and
ball on downthrown side
Quaternary and
Tertiary deposits
Late Cenozoic
right-lateral fault—
Arrows show direction
of movement
Mesozoic
plutonic rocks
Precambrian to Jurassic
sedimentary and
volcanic rocks
Jurassic (East Sierran)
thrust fault—Dotted
where concealed.
Sawteeth on upper plate
Late Permian
thrust fault—Dotted
where concealed or
intruded. Sawteeth on
upper plate
Late Permian
overturned syncline
Early Permian
thrust fault—Dotted
where concealed or
intruded. Sawteeth on
upper plate
Figure 1. Generalized geologic map showing location of Cerro Gordo Peak 7.5' quadrangle in southern
Inyo Mountains, California. CM, Conglomerate Mesa; EIFZ, Eastern Inyo Fault Zone; FT, Flagstaff
Geologic ackground:
Thrust;BHMF,
Hunter Mountain Fault; ICT, Inyo Crest Thrust; LCT, Last Chance Thrust; LFT, Lee Flat
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Star,
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Los Angeles in the Inyo Mountain Range f tmodified
he western Basin and (1997)
Range Province. on recent studies by the authors; parts of these fault traces are speculative.
To the west of the district is Owens Valley, a structurally controlled valley at the eastern front of the Sierra Nevada Mountains. Cerro Gordo is one of several lead-­‐
silver-­‐zinc districts in a 100 mi trend extending from Cerro Gordo, Inyo Mountains 2
to Tecopa District, Nopah Range. Rocks of the Inyo Range consist of strongly folded and faulted Ordovician to Middle Triassic sedimentary rocks that were intruded by granitic bodies and aplite dikes followed by abundant andesitic and dacitic dikes. Paleozoic rocks are over 11,000 feet thick and are dominantly carbonates. Triassic rocks are approximately 4,000 feet thick, with the lower half of the section comprising carbonates and marine clastics, and the upper half of the section comprising volcanics. The most significant structural feature is the south-­‐plunging asymmetrical Cerro Gordo anticline. Smaller folds within the From left to right: J. Mizer, D. Favorito, and S. O’Neal looking at core from the Cerro Gordo Mining District, California. Photo by J. Dabbs, 2015. anticline vary greatly in magnitude and tightness, with many directly related to reverse faulting. In general, faults strike from N-­‐S to NW-­‐SE and consist of both reverse and normal faults. Folding and thrusting within the region occurred after the deposition of Middle-­‐Triassic strata, indicating either Late Jurassic or Early Cretaceous deformation. Later Cenozoic regional extension resulted in widespread normal and strike-­‐slip faulting and volcanism. Thus, most of the sedimentary rocks in the Cerro Gordo area have been either metamorphically or metasomatically altered. Local areas of intense contact metamorphism commonly occur, particularly in contact with the Ignacio (hornblende-­‐quartz monzonite porphyry) and Cerro Gordo (monazite porphyry) stocks. Mineralization: Silver, lead and copper ore occurs in quartz veins that strike northwest, inclined pipes, shoots in fissures, small isolated pockets, and massive ore Tetrahedrite with copper-­‐oxide in quartz matrix, Cerro Gordo Mining District. Photo by J. Dabbs, 2015.
bodies. Major lead-­‐zinc ore bodies in the district are fracture-­‐
controlled sulfide ore replacement chimneys in a fracture zone related to the Cerro Gordo fault. Ore bodies occur in the marble of the Devonian Lost Burro formation, located in the east side (footwall) of the N-­‐S striking Cerro Gordo normal fault. The two principal ore channels, the Jefferson and Union chimneys, plunge steeply to the south and occur in fractured marble close to the Cerro Gordo fault. Replacement and alternation associated with smaller intrusives is also common, particularly the Jefferson diabase dike and other andesitic to dacitic dikes and sills. Later ore mineralization occurred in siliceous Nontranite (possibly from sulfide weathering of andradite) surrounding Fe-­‐sulfide bearing quartz vein with associated copper oxides in a prospecting trench, Cerro Gordo Mining District. Photo by J. Dabbs.
veins (the San Filipe and Santa Maria veins) containing galena-­‐tetrahedrite-­‐barite ores within a quartz matrix. Upper units of Lost Burro marble also contain supergene zinc-­‐carbonate ore bodies that broadly occur along bedding. Massive smithsonite extending approximately 100 ft laterally from the Union Chimney lead-­‐silver ore body has been mined as zinc ore. Most production, however, came from massive silver-­‐lead ore that consisted of argentiferous galena along with lead carbonates and sulfates. Mining operations were carried out in the Cerro Gordo district from 1866 to 1957. Commodities produced include silver, gold, lead, zinc and minor amounts of copper. The Cerro Gordo mine accounted for the majority of the district’s production. During the mine’s peak year of production in 1874, an estimated 4,400,00 ounces of silver, 37,000 tons of lead, and 12,000 tons of zinc were produced. Other workings include the Union, San Filipe, Morning Star, Belmont, Newsboy, Newtown, Ella, and Perseverance mines. Accessibility: Terrain is exceptionally steep and rugged. Four-­‐wheel drive is required. Many underground workings in the area are collapsed and are not safe for touring. Property is privately held, and permission from owners is required for entry. For more information, contact Robert Wetzel.