Tonkin Springs Mine, Tonkin Spring, Tonkin, Antelope Mining District, Eureka County, Nevada, USAi

Regional Level Types
Tonkin Springs Mine	Mine
Tonkin Spring	Spring
Tonkin	- not defined -
Antelope Mining District	Mining District
Eureka County	County
Nevada	State
USA	Country

A bio-leaching operation gold mine. Mill has a 1,500 tons/day carbon-in-leach mill.

Structure: Intercalated slices of eastern and western facies rocks comprise the upper plate of the Roberts Mountains thrust. Brecciation and recumbent folding resulting from late Devonian to Mississippian deformation are well developed within the tectonically disturbed zone between slices. En echelon NNW-striking, east dipping normal faults of Tertiary age dominate the local structural fabric. ENE-striking, near vertical normal faults are subordinate in magnitude to the NNW trend and have localized silicification in places (e.g. Rooster Ridge). A N-S to NNE structural trend is recognized on high altitude photography. Roberts Mountains Thrust; WNW-striking broad, open folds.

Alteration: Alteration that has affected ore host rocks includes silicification, decalcification, argillization, carbonization. Silicification is widespread throughout the district and is evidenced by abundant jasperoid. Gold ore is often found in decalcified limestone. Argillization is widespread, but argillized rocks are generally not mineralized. The amount of carbonaceous ore has now been shown to be at least in part due to finely disseminated sulfide, not carbon.

Commodity: Ore Materials: pyrite, arsenopyrite, native gold, Gangue Materials: realgar, orpiment, cinnabar, stibnite, quartz, calcite, barite

Deposit: Approximately 75% of gold occurs as micron-sized grains in pyrite and arsenopyrite. 25% of gold occurs as free grains in silica veinlets or along fractures.

Deposit type: Sediment-hosted Au

Development: Exploration began in the Tonkin Springs area during the 1950s and 1960s. The Rooster claims were staked in 1966 by Lyle Campbell on the basis of outcropping jasperoid. Claims optioned by several companies 1966-81, with additional staking expanding the claim block during this period. Companies which conducted exploration during that time, included Homestake Mining, American Selco, Chevron Resources, Placer Amex, Earth Resources and Freeport Exploration. These companies discovered gold mineralization but considered to be too low-grade and sporadic at that time to be of interest . Mineral Ventures, Inc. conducted a drainage sediment sampling program in 1979. Anomalous gold concentrations were identified on the Rooster claims and for several miles to the south. Drainages in the immediate vicinity of the Tonkin Springs deposit contained gold contents varying between 0.03 and 0.06 ppm. The Rob claims were then staked in 1980. Precambrian Exploration teamed with Mineral Ventures, Inc. in 1982 to explore the Rob Claims. Geologic mapping and grid soil and rock geochemical surveys defined the drill targets that became the TSP 1,3, and 4 orebodies. These shallow ore pods had coincident Au, Hg, As, and Sb soil anomalies (see Mehrtens, 1987). Silver State Mining (now U.S. Gold) optioned the property in January 1985 and put the property into production. The first gold was poured October 1985. The land position was expanded by the optioning of the Rooster claims in 1986 and claim staking in the Twin Peaks area in 1987. The claim block in 1990 encompasses approximately 42 square miles along trend. A joint venture of U.S. Gold (49%) and Homestake Mining (51%) was formed in early 1991 to further explore and develop Tonkin Springs. According to Silver State Mining 1985 annual report, total capital costs are $1.90 million, production costs are $85/oz. Au ($122/oz. Au, including depreciation, depletion, and amortization), and gold recovery rate is 70%. U.S. Gold is pioneering bio-oxidation of bulk gold ores at Tonkin Springs. From 1981 to 1985, Energy Reserves Group and Mineral Ventures continued to explore the property until their mining leases were terminated. In January, 1986 US Gold Corporation leased the property and has controlled it ever since. Exploration in the area that hosts the sulfide deposits began in 1979. At this time, Mineral Ventures conducted sampling program searching for Carlin-type gold deposits. In 1981, Mineral Ventures conducted a drilling program that encountered potentially economic mineralization at what later became known as the TSP-1 deposit. The company continued exploration drilling and, in 1985, US Gold entered into a joint venture on the property with Mineral Ventures. In 1987, US Gold bought control of the company. The drilling completed by US Gold from the mid to late 1980s delineated several more small deposits. Mining activities took place that produced over 30,000 ounces of gold, mostly from oxide ores. During the work, many roads were constructed and heap leach pad was built and operated. From 1998 to 1990, in excess of $30 million was spent constructing an on site mill. Many more claims were added to the property position and several exploration targets were found. From 1991 to 2001, US Gold teamed up with several mining companies to explore the property. Some of the companies included Homestake Mining, Gold Capital, Globex Mining and Agnico-Eagle. Each of these companies conducted an exploration program which laid out different goals. Homestake drilled 86 reverse circulation and core holes. Though several interesting showings were encountered in this drilling, Homestake determined it had not discovered a deposit that met its corporate objectives and, in 1992, it withdrew from the joint venture. In 1993, Gold Capital attempted to modify the existing heap leach pad but ran short of financial resources. In February, 1999 it sold its interest to Agnico-Eagle. From 1993 to 1999, little exploration took place on the property. Agnico-Eagle drilled 107 reverse circulation holes and confirmed the mineral resource at Tonkin Springs. It also extended the known mineralization at various deposits on the property and discovered new gold mineralized zone at the north end of the property. Aginco-Eagle did not find enough economic mineralization to justify its goals and, in October, 2001, also withdrew from the joint venture. In 2003, BacTech acquired a 55% interest in the property from US Gold. However, BacTech was unable to fulfill the requirements set out in the agreement, giving US Gold 100% ownership over Tonkin Springs. In July 2005, Rob McEwen purchased 33% of US Gold and also assumed the position of Chairman and CEO. http://www.romarco.com/news/index.php?&content_id=131 The Tonkin Springs Mine is a previously producing gold mine strategically located in the prolific Cortez Gold Trend of Nevada. The property package encompasses 36 square miles and has existing infrastructure including a 1,800 tonne-per-day mill on site. It is anticipated that a feasibility study will be conducted immediately for start up operations. Strategically located on the Cortez Gold Trend south of the Placer Dome:Rio Tinto Cortez Joint Venture's Pipeline deposit and the recently discovered Cortez Hills deposit In operation from 1985 to 1988 and again in 1990 Existing mill and infrastructure (+$30 million original cost) 36 square mile land package provides exploration potential

Geology: Intrusive sills of intermediate composition are spatially associated with gold deposition. Since the sills are offset by feeder faults and can be mineralized, they are believed to pre-date gold deposition. The sills may have acted as impermeable caprocks to the hydrothermal system, resulting in the localization of gold in the sediments adjacent to the intrusive.

Ore(s): The principal ore control is structure. All known orientations of high angle normal faults as well as lower angle thrust fault-related brecciation served as plumbing for the hydrothermal system. The NNW-striking set of normal faults defines the most noticeable trend of mineralization on the district level; higher grade pods usually flow this direction. The N60E set of normal faults is second in importance and serves to control mineralization at the individual pits. N-S control of mineralization is suggested by gold-in-soil anomalies and by subsurface gold mineralization in the Rooster main area.

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Link to USGS MRDS:	10310543

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References