Abstract Within the central part of the Sulphur Creek Mining District six epithermal gold-mercury deposits have been mined, the West End, Central, Cherry Hill, Empire, Manzanita, and Wide Awake (Fig. 1). The mining district also includes the Abbott, Elgin and Rathburn mercury deposits and several hot springs that are depositing gold and cinnabar. The association of gold and mercury in the district was recognized early and gold was mined at the Cherry Hill and the Manzanita Mercury Mine from 1865 to 1891 with total production being about 3,000 oz of Au (Whitney, 1865, and Bradley, 1916). Whitney (1865) describes cobbles of cinnabar from the Sulphur Creek Mining District containing plumes of gold distributed through out the cinnabar. Fine placer gold is also present in drainages within the Sulphur Creek district, but has not been mined. Total mercury production from the district has been about 33,000 flasks, primarily from the Abbott mine. The Wide Awake mine was reported to have reserves of 24,000 flasks in 1899 and substantial unreported production may have come from this mine. In 1977, Homestake Mining Co. delineated a small gold deposit in the area of the Cherry Hill, West End, and Wide Awake Mines. The mineralization extends under the Sulphur Creek valley which separates these mines. Although numerous high-grade gold veins are present, typically greater than 0.3 oz of Au with multiple oz assays common, the veins are widely spaced and the deposit is presently uneconomic.

ABSTRACT This field trip explores the geology and mining history of the Bodie Hills with a focus on the Bodie and Aurora mining districts. The field trip starts and ends in Bridgeport, California. Our first geologic stop is at Travertine Hot Springs, which provides an analogy for the style of mineralization observed in the Bodie and Aurora districts. We then proceed south on Highway 395 to the Bodie exit at Highway 270. At this location on Highway 395 is the placer camp of Dogtown with outcrops of till from the Sherwin glaciation. A side trip up Cinnabar Canyon exposes rocks with veinlets of cinnabar and silicic alteration. From here, we travel through several different components of different stratovolcanoes and arrive at the preserved ghost town of Bodie. Bodie Bluff and Standard Hill contain most of the mine workings for the Bodie district. At Bodie we discuss different interpretations of volcanic history and stratigraphy and learn about the U.S. Bureau of Land Management’s 1997 economic appraisal of the mineralization there: 69.8 million tons of ore averaging 0.4 oz/ton Au. Leaving Bodie, we pass through a placer field where William Bodie made his discovery of the mine and the district that bears his name. And then we move through the Bodie volcanics to those volcanic rocks associated with Aurora. On the way to Aurora, we will see the stage stop site of Del Monte. At Aurora, we view the active open pit mining operation and compare this district with Bodie and others in the Bodie Hills. Both Bodie and Aurora were classified as principal gold deposits of the United States.

ABSTRACT The California Coast Ranges mercury deposits are part of the western North America mercury belt, in which mercury occurs most commonly as red cinnabar (α-HgS), sometimes associated with its high-temperature polymorph, metacinnabar (β-HgS). In the Coast Ranges, ores were deposited from hydrothermal solutions and range in age from Miocene to Holocene. Ore deposition at Mount Diablo generally occurred along active faults and associated extension fractures in the Franciscan complex, most often in serpentinite that had been hydrothermally altered to silica-carbonate rock. The Mount Diablo mine lies ~48 km (~30 miles) northeast of San Francisco in Contra Costa County and is mineralogically unique in California, because metacinnabar, the higher-temperature polymorph of mercury sulfide, is a major primary ore mineral in the deposit, while at all other mercury mines in California, it is quite rare. In addition, hydrothermal activity is so recent that sulfurous gases and methane continued to be released into the mine at least into the 1940s. Historically, long before active large-scale mining began in the 1800s, the Mount Diablo mercury deposits were known to the Indigenous people of the Ohlone tribes, who used the cinnabar in rituals as well as for red pigment to decorate their bodies, and as a prized trade item. The deposit was later rediscovered in 1863 and mined intermittently until 1958. The Mount Diablo mine and adjacent Rhyne (also variously spelled Ryne or Rhine) mine were the sites of most of the mercury operations in the region, and at both mines, mercury ore occurs in structurally controlled lenticular bodies of silica-carbonate rock and serpentinite. The total district production probably exceeded 12,300 flasks (at 76 pounds or ~34.5 kg per flask) at an estimated grade of 2711 g per metric ton. Low-grade ore reserves are believed to still exist, with 17,000 short tons of indicated and inferred ore. Other minor deposits of copper, silver, and gold occur on Mount Diablo, principally in and around Eagle Peak, but mercury is not associated with these deposits. The most serious environmental problem associated with the mercury mines is the transport of mercury via mine drainage from the Mount Diablo mines to Dunn Creek, a tributary to Marsh Creek, which ultimately drains into Suisun and San Francisco Bay. The concern is that elemental mercury (Hg 0 ) and the mercury ion Hg(II) can be biologically converted to toxic monomethylmercury (MeHg). To combat this problem, a long-term process of mine remediation has been undertaken.

Abstract Sulphur Bank is the most productive mineral deposit in the world that is clearly related to hot springs. The ore is late Quaternary and is localized in rocks immediately below the water table that existed prior to mining. The hydrothermal alteration and the mineralogy of the veins have been controlled largely by the water table. The upper part of an andesite flow has been above the water table and is extensively altered by sulfuric acid formed by oxidation of H2S. Characteristic alteration minerals are opal, cristobalite, and anatase where leachi ng has been intense, and kaolinite, halloysite, alunite, soluble sulfates, and perhaps jarosite and montmorillonite where acid attack has been less intense. Native sulfur without cinnabar was abundant near the surface, but, as the water table was approached, sulfur decreased, and cinnabar became abundant. The principal ore bodies were at and below the water table and consisted of cinnabar, marcasite, pyrite, dolomite, calcite, quartz, a zeolite mineral, and all the minerals of the original rocks. Metacinnabar and stibnite were locally common. The waters deep in the spring system appear to be nearly neutral, but near the water table they become slightly acid because of mixing with downward percolating waters containing H 2 SO 4 resulting from oxidation of H 2 S. Films of condensate in the areas of most intense acid leaching may have pH values of 1 or less. The present thermal waters are very highin total CO 2 , boron, ammonia, sodium, and iodine and are low in silica and potassium as compared to many thermal and mineral waters. Chemically and isotopically they are unlike most thermal waters associated with recent volcanism. The present rate of discharge of water of deep origin is calculated to be about 50 gpm. T h e average concentration of quicksilver in the ore solutions was probably 0.05-8 ppm, assuming an interval of deposition between 10,000 and 100,000 years and a rate of discharge of water of 50–1000 gpm. The most reasonable estimate is believed to be 0.1–1 ppm. Present temperatures are relatively low compared to other hot-spring systems of clearly volcanic origin . The present heat flow is on the order of 200,000 cal per sec, or about 12 times “normal” for the area; total heat flow inthe past may have been as much as 20 times as much. The heat is almost certainly volcanic in origin, but, despite association with Quaternary volcanic rocks and volcanic heat, the chemical and isotopic compositions of the water and gases now being discharged indicate that these fluids are nonvolcanic i n origin.