Dewdrop Gold Project
Yerington Mining District, Lyon County, Nevada
- Epithermal gold and porphyry copper exploration targets in the Yerington district, northern Walker Lane Gold Belt, Nevada
- 159 unpatented mining claims (3,134 acres) with numerous historic workings
- Multiple high-grade rock samples with up to 7.31 g/t gold, 4.7% copper and historic assays up to 46 g/t gold
- Historic work focused on Jurassic porphyry copper exploration and ignored younger Miocene epithermal gold occurrences that form significant deposits elsewhere in the northern Walker Lane Gold Belt (e.g. Aurora-Borealis and Comstock Lode)
The Dewdrop project is located in the Gray Hills approximately 15 kilometers southeast of Yerington, Nevada. Access is via maintained county roads and dirt roads in permit-friendly Bureau of Land Management tenure. Elevations range from approximately 4500 to 6500 feet with sparse high desert vegetation typical of the western Great Basin. The Dewdrop project is 45 km NNW of the Borealis mine complex (1.1 Moz Au)1, 65 km SE of the Comstock Lode (8.25 Moz Au, 192 Moz Ag)2, and 10 km south of Nevada’s newest copper mine, Pumpkin Hollow (23.9 Mt at 1.74% Cu)3. The district also includes the Ann Mason, MacArthur, Bear, and Yerington porphyry copper deposits for a total copper endowment of over 3.6 Bt at 0.39% Cu (Fig. 1)3,4.
Figure 1 – Location map of the Dewdrop project displaying Zacapa’s land position in the Yerington District south of the Pumpkin Hollow Mine. Zacapa’s controls 159 claims covering over 3,100 acres3,4,5
Zacapa assembled the Dewdrop project through a combination of staking and purchases from private parties. Mineral occurrences were first documented in the region in the early 1860’s and the first mining at what would become the Yerington porphyry deposit occurred in 1907. Through the mid- to late-1900’s Anaconda was most active in the region at Yerington (1.6 Bt @ 0.43% Cu), MacArthur (398 Mt @ 0.21% Cu), and Ann Mason (1.4 Bt @ 0.32% Cu), with other exploration by Phelps Dodge at Bear (500 Mt @ 0.4% Cu) and U.S. Steel at Pumpkin Hollow (355 Mt @ 30% Fe, 0.61% Cu)*. Most exploration was focused on porphyry deposits in the Singatse Range. To the southeast in the Gray Hills, prior exploration and small-scale mining was focused on the Flyboy copper-gold-uranium prospect and the Coyote and Poison Rock gold prospects. Previous explorers included Hudbay and Convergent Mining, with no known drilling.
The project area is in the northern Walker Lane Gold Belt near the southern extent of the Ancestral Cascades Arc, an area with a number of Jurassic porphyry copper deposits and Miocene epithermal gold deposits6 (Fig. 2). Folded and weakly metamorphosed Triassic-Jurassic sedimentary and volcanic rocks were intruded by numerous plutons associated with mid-Jurassic arc magmatism. Two major batholiths have been documented in the Yerington District, the older ~169 Ma Yerington batholith which generated at least four porphyry copper deposits and associated skarn mineralization, and the younger ~165 Ma Shamrock batholith7. These intrusions and their affiliated hydrothermal systems also created extensive Na-Ca alteration (albite-epidote-actinolite) and iron-oxide mineralization interpreted as an indication that evaporitic brines from the sedimentary sequences were mobilized by the hydrothermal cells8. Compressional tectonics and uplift created a major erosional unconformity between Jurassic rocks and overlying Oligocene volcanic rocks deposited ~26 Ma (Mickey Pass and Singatse tuffs). Subsequent extensional faulting accommodated additional Miocene volcanic and sedimentary units in fault bound basins, while also rotating the Mesozoic rocks 60-90° and exposing a 7 km deep cross section at the present surface in the Yerington area9. Miocene volcanic rocks were contemporaneous with the formation of significant epithermal Au-Ag deposits in the northern Walker Lane Belt (e.g. Comstock, Aurora-Borealis, and Rawhide).
Exposures in the Dewdrop Project/Grey Hills area are dominated by a variety of granitic intrusive rocks, concealed in large areas by Oligocene-Miocene volcanic rocks and interleaved sedimentary successions (Fig. 3). The intrusive rocks have been interpreted as Jurassic quartz monzonite of the Gray Hills pluton, part of the Shamrock batholith9, which is cut by numerous dikes. These granitic rocks are unconformably overlain by 27-26 Ma tuffs (Mickey Pass and Singatse Tuff), each more than 100 meters thick. These are unconformably overlain by the 15-14 Ma Lincoln Flat Andesite and thick fault-bound accumulations of Wassuk Group sedimentary rocks and minor basalt flows. The initiation of extensional and right-lateral faulting coincided with eruption of the Lincoln Flat Andesite, which is considered to be synchronous with structurally controlled epithermal alteration and gold mineralization.
Figure 2 – Map of the southern Ancestral Cascades Arc segment showing epithermal deposits and quartz-alunite alteration zones within Walker Lane domains (C, Carson; G, Goldfield; IM, Inyo-Mono; MD, Mina deflection; MP, Modoc Plateau; PL, Pyramid Lake; SF, Sierra Front; WL, Walker Lake). Modified from John et al., 20156.
Figure 3 – Generalized geologic map of the Grey Hills and surrounding Yerington area with Mesozoic felsic plutonic rocks shaded green within Zacapa’s 2022 exploration area (blue outline). Modified from Surpless et al., 200210.
Alteration and mineralization at Dewdrop can be broken down into several styles (Figs. 4, 5):
- Gold-bearing structures consist of quartz veins with pyritic argillic alteration halos and elevated As, Hg, and Sb. These mineralized zones have variable copper concentrations and contain gold values of 1-2 g/t in the veins and over 7 g/t in the alteration halos. Unconfirmed historic assays of over 46 g/t Au and visible gold have been reported. The mineralized zones occur in discrete pods within interpreted structural corridors that extend over strike lengths up to 5 km.
- Copper mineralization occurs principally in western portions of the property where porphyry-style sheeted swarms of biotite-bearing quartz-pyrite-chalcopyrite veinlets occur in strongly albite altered porphyritic quartz monzonite at the Flyboy prospect. The veinlets are subhorizontal suggesting significant post-mineral rotation. Outcrops are strongly coated by copper-oxides and contain up to 4.7% Cu and 1 g Au with associated Ag, Cd, Se, Te, and Zn. In the center of the property at the Io and Showdown prospects copper also occurs in discrete epithermal(?) quartz veins and in thin chalcopyrite bearing veinlets in magnetite-biotite altered host rock. On the east side of the property copper occurs in association with iron-oxide and quartz/tourmaline breccias.
- The property also displays widespread albite-epidote-actinolite alteration reminiscent of IOCG style assemblages.
Jurassic porphyry copper systems and associated skarn (e.g. Yerington, Ann Mason) overprinted by younger Jurassic intrusions and much younger Miocene (< 20 Ma) epithermal Au-Ag mineralization associated with the northern Walker Lane Gold Belt (e.g. Comstock lode).
- Flyboy – outcropping copper-oxides associated with sheeted quartz-biotite veins in porphyritic quartz monzonite
- Coyote – well defined N-S trending gold-bearing vein system
- Io – epithermal gold veins with illite-pyrite alteration halo, within a larger zone of magnetite-biotite altered host rocks and local albite-epidote-actinolite alteration
- Showdown – epithermal copper-gold veins and numerous less explored copper occurrences
- Hacksaw – copper bearing iron-oxide + quartz/tourmaline breccias and several discrete epithermal copper-gold rich veins
PERMITTING AND ESG
- All land administered by the U.S. Bureau of Land Management
1 Welsh, J.D., Brown, J.M., Willis, D., and Seal, T., 2011, NI 43-101 Pre-feasibility study update of the mineral resources of the Borealis Gold Project located in Mineral County, Nevada, USA: Gryphon Gold Corp., 262 p.
2 Vikre, P.G., 1989, Fluid-mineral relations in the Comstock Lode: Economic Geology, v. 84, p. 1574-1613.
3 Nevada Copper, Prefeasibility Study for Pumpkin Hollow Project, Yerington, Nevada, January 21, 2019.
4 Lion Copper and Gold, NI 43-101 Resource Estimate for MacArthur Copper Project, Mason Valley, Nevada, February 25, 2022
5 Hudbay Minerals, Preliminary Economic Assessment for Mason Copper Project, Yerington, Nevada, April 6, 2021
6 John, D.A., du Bray, E.A., Henry, C.D., Vikre, P. G., Pennell, W., and Garside, L. J., 2015, Cenozoic magmatism and epithermal gold-silver deposits of the southern ancestral Cascade arc, western Nevada and eastern California: New Concepts and Discoveries: Geological Society of Nevada 2015 Symposium Proceedings: Reno, Nevada, Geological Society of Nevada, p. 611-645.
7 Dilles, J.H., Einaudi, M.T., Proffett, J.M., and Barton, M.D., 2000, Overview of the Yerington porphyry copper district: Magmatic to nonmagmatic sources of hydrothermal fluids: Their flow paths and alteration effects on rocks and Cu-Mo-Fe-Au ores: Society of Economic Geologists Guidebook Series, v. 32, p. 55-66.
8 Runyon, S.E., Barton, M.D., Dilles, J.H., Ohlin, H.N., Seedorff, E., Carpenter, K., … and Garside, L.J., 2015, Iron oxide-rich mineralization and related alteration in the Yerington district, Lyon County, Nevada: New concepts and discoveries, Geological Society of Nevada, Symposium, Reno/Sparks, p. 251-283.
9 Surpless, B.E., 2012, Cenozoic tectonic evolution of the central Wassuk Range, western Nevada, USA: International Geology Review, v. 54, p. 547–571.
10 Surpless, B.E., Stockli, D.F., Dumitru, T.A., and Miller, E.L., 2002, Two-phase westward encroachment of Basin and Range extension into the northern Sierra Nevada: Tectonics, v. 21, no. 1.
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