• Gold: Average grade 0.3 ounces per ton (10.3 g/t)
• Silver: Average grade 30.0 ounces per ton (103.4 g/t)
One mile north of Central Tonopah District
Exploration Potential Similar to Central Tonopah (1.9M oz. gold, 174M oz. silver)
Estimated Ore K and Q Veins: Up to 120 tons. (24,000 oz. gold, 2.4M oz. silver
Over 27,000' of core and reverse circulation drilling
8 unpatented claims totaling 160 acres in a mining friendly jurisdiction
The Walker Lane Trend hosts some of the most famous gold and silver deposits in Nevada, including the Comstock, Bullfrog, Goldfield, central Tonopah and Round Mountain districts and has produced more than 35 million gold-equivalent ounces. Round Mountain, 50 miles to the north of King Tonopah, continues to be one of the largest producing mines in Nevada.
The King Tonopah Gold and Silver Project consists of 8 unpatented claims (160 acres) located one mile north of the town of Tonopah in the Tonopah Mining District, Nye County, southwestern Nevada.
In January, 2005 Tonogold Resources signed a 10 year mining lease, with option to purchase, eight claims in the King Tonopah Gold and Silver Project.
1901 through 1980's
From 1901 through the mid-1950's, the central Tonopah District produced 8,750,000 tons of ore averaging 0.23 opt gold and 23 opt silver ($267/ton today), for 1,861,200 oz. gold and 174,152,628 oz. silver (Bonham and Garside, 1979, p. 109) and a total value at today's metal prices of $2,070,000,000. Peak annual production in 1913 totaled 574,542 tons of 0.22 opt Au and 20 opt silver ($241/ton today). At least 95% of Tonopah's historical production came from a zone one mile east-west, 1,200 feet north-south, and over 2,000 stratigraphic and vertical feet directly beneath the town of Tonopah.
The King Tonopah shaft was sunk for exploration purposes around 1905 to test the outcropping Mizpah Andesite, host for much of the Central Tonopah ores. The shaft bottomed just below the 300 foot level (elevation 5,885 feet) without encountering ore, but it did pass through now-significant wallrock alteration. After exhaustive underground study of the Tonopah District, Nolan (1935) speculated on several areas for further exploration, the most favorable being "the region to the north" centered on the area around the King Tonopah shaft.
In 1947, Calumet-Hecla's field geologists, following Nolan's (1935) lead, found quartz-adularia-sericite vein material on the King Tonopah dump and recommended drilling. Eight holes were drilled by Calumet Hecla under the name of Tonopah Development Company. The fourth drill hole (ADH-4) intercepted two veins with typical Tonopah-type alteration and mineralization, the Q and K veins.
The first ADH-4 intercept (Q vein) was at an elevation of 5,405 feet and assayed 0.058 opt Au and 5.3 opt Ag over 9.0 vertical feet. The second ADH-4 intercept (K vein) was at an elevation of 5,330 feet and assayed 0.098 opt Au and 9.6 opt Ag over 13.3 vertical feet. Calumet-Hecla's drill hole ADH-6 also had two intercepts: the first (Q vein) at an elevation of 5,395 feet graded 0.066 opt Au and 12.0 opt Ag over 4.0 angle feet, and the second (K vein) at an elevation of 5,365 feet graded 0.119 opt Au and 22.7 opt Ag over 16.5 angle feet. Two more holes were drilled by Calumet-Hecla before the property was optioned to Asarco. Asarco drilled four additional holes (ADH-9 through ADH-12) in 1948 and returned the property to Calumet-Hecla.
In 1952, Summit King & Homestake joint ventured the King Tonopah property from Calumet-Hecla, then refurbished the King Tonopah shaft to the bottom at the 300 Level and drove a cross-cut 1,100 feet to the north. In April, 1952, Summit King-Homestake the crosscut encountered five feet of "high grade" argentite-pyrargyrite vein (King Tonopah "K" vein) with the "traditional Tonopah ratio of 100 parts silver to 1 part gold" (Tonopah Times-Bonanza, April 22, 1952). By December, 1952, Summit King-Homestake drove east and west for a total of 300 feet on the 300 Level, encountered offsetting faults at both faces, and then began to develop the King Tonopah vein at depth after sinking an internal winze. Summit King-Homestake did not attempt to develop or explore the Q vein running parallel to the K vein about 30 to 50 feet to the north.
On January 2, 1953 (Tonopah Times-Bonanza), Summit King-Homestake declared the fault offsetting the east end of the King Tonopah vein was a "Halifax-style fault dipping 35º to the northeast". The Halifax Fault is a Central Tonopah feature. The west end of the exposed King Tonopah vein terminated against a northeast-striking vertical fault. Of the 300 feet developed between the two faults, "260 feet were vein matter with good values" (Tonopah Times, 2 Jan. 1953).
By October 23rd, 1953 (Tonopah Times-Bonanza), the Summit King winze had reached the 650 Level. An "ore width" of four feet was encountered on the 550 Level. About 15,000 tons averaging about 0.3 opt Au and 30 opt Ag was blocked and mined from the K Vein between the 550 and 200 Levels by July 1954 (Bonham & Garside, 1979, page 120). In a slightly conflicting report on production, Wilkins (1986, page 4) states that 30,000 tons grading 0.02 opt Au and 20 opt Ag were mined during this period. Under either scenario, low metal prices at the time were the governing factor in Summit King-Homestake's subsequent decision to return the lease to Calumet-Hecla.
Summit King-Homestake did not explore beyond the offsetting faults along strike to the east and west, nor did they develop the King Tonopah vein below the 550 Level, deciding instead to take what profit they could during what became a prolonged period of low metal prices. All of the Summit King-Homestake production came from approximately 50% of the faulted segment of the K vein between the 550 and 200 levels, most of which was four to five feet wide. No attempt was made to produce from, or even evaluate, the adjacent and parallel Q Vein.
Calumet-Hecla gave several leases to local miners between 1954 and 1958, who reported shipping ores valued at $40 per ton to the smelter at McGill, Nevada. The last reported attempt to fully develop the King Tonopah vein occurred in 1958 and 1959, when the directors of U.S. Milling and Minerals (Silverpeak mill) formed the Tonopah King Mining Company and leased the King Tonopah mine and surrounding claims. Their first shipment was made in December, 1958 (Tonopah Times-Bonanza), and periodic shipments continued from 1958 to 1962, when the Silverpeak mill closed after a series of fatal accidents. The King Tonopah shaft and headframe burned in the late 1960's.
Summa Corporation and Hughes Tool Company consolidated ownership of patented and unpatented claims within the Tonopah Mining District in the late 1960's. After acquisition, Summa focused exploration and development capital in the central Tonopah District. They did not drill the area around the King Tonopah mine.
In 1977, Houston Oil and Minerals ("Houston") acquired all of Summa's Nevada mineral properties, including the consolidated patented and unpatented claims in the Tonopah Mining District. Houston's priorities for developing the Tonopah District during rising metal prices included: 1) exploitation of the considerable values already at the surface in the historical waste dumps and tailings, 2) development of open-pittable reserves in the central Tonopah District, and 3) exploration of potential new underground resources, especially in the northern Tonopah District.
Houston Oil and Minerals Inc. concluded Tonopah's surface resources could be brought into production, and potential subsurface resources could be developed as experience was gained and exploration proceeded within the District. In 1979, Houston was purchased by Tenneco Inc., who cancelled many of Houston's exploration and development projects. Fortunately, Houston was able to complete their geologic mapping surveys, surface geochemical surveys, dump sampling surveys, and some drill programs prior to the complete cancellation of their Tonopah District project.
Houston's drill program in the northern Tonopah District consisted of thirteen core holes (HT-1 to HT-13). Houston discovered extensions of the K (King Tonopah) and Q veins and six new vein or vein stringer zones. Orientations of some of these new intercepts are not well known. Vein intercepts along the K and Q veins assayed up to 0.295 opt Au and 16.3 opt Ag. One of the six possible vein-bearing structures was an 11-foot wide quartz-sulfide stringer zone encountered 1,200 feet north of the King Tonopah vein. This interval, in vertical core hole HT-11 at an elevation of 5,340 feet assayed 0.10 opt Au and 2.5 opt Ag. The HT-11 intercept is an excellent indicator of additional Tonopah-type veins in the Northern Tonopah District. The other three vein and stringer intercepts away from the original K and Q veins (HT-5, HT-7, and HT-13) are also good indicators. Follow-up drilling of these intercepts or of the indicated vein system was not undertaken by Houston or its successor Tenneco.
In summary, drill holes at King Tonopah have encountered four steep vein structures in addition to the steeply-dipping K and Q veins. The structural concept at King Tonopah strongly suggests at least one shallow and west-dipping, fault-vein similar to the Central District's "Tonopah Fault" somewhere below the steep vein intercepts. The Tonopah Fault was a high-tonnage source of production for the Central District. A similar foundational structure should be a priority during future exploration at King Tonopah.
The productive veins of King Tonopah and the Central Tonopah District are near-duplicates. They occur in the same host rocks, share the same structural patterns, alteration assemblages, mineral character, trace elements, and 100/1 silver-gold ratio. This conclusion was first expressed and recommended by Nolan (1935).
The surrounding districts are characterized by early Paleozoic shale, siltstone, and minor chert and limestone and Mesozoic granitics. These same basement units are undoubtedly at depth beneath Tonopah, but have not yet been encountered by either drilling or underground workings. Tonopah's Tertiary volcanic hosts vary greatly in thickness and areal extent, a characteristic of the caldera environment. Thicknesses mentioned here may be regarded as average. As expected, Tertiary units are often separated by district-scale unconformities.
The basal Tonopah Formation consists of 1,000 feet of orange to pink to grey, partially welded, Oligocene lithic ashflow tuff, volcanic breccias, and banded rhyolite domes and flows. The Tonopah Formation is unconformably overlain by the 2,000-foot thick Miocene Mizpah Formation. The Mizpah Formation consists of purplish-brown to black, porphyritic andesite to trachyandesite flows, breccias, and minor dacite intrusions. Feldspar phenocrysts are often white and euhedral. Mizpah andesites are unconformably overlain by the Fraction Tuff.
The Miocene Fraction Tuff, often more than 600 feet thick, consists of two or more rhyolite cooling units with lithic ashflow tuffs, tuff breccias, and minor interbedded siltstone and sandstone. The Miocene Heller Tuff is a more geographically constrained but mappable crystal-rich, quartz latite ashflow tuff above the Fraction Tuff. The Heller and Fraction tuffs are unconformably overlain by the Miocene Seibert Formation, a district-wide sedimentary unit locally greater than 300 feet thick consisting of poor to well-sorted volcanic siltstone, sandstone, and conglomerate.
The Oligocene Tonopah rhyolites and Miocene Mizpah andesites are hosts for Tonopah-type quartz-adularia-sericite epithermal gold-silver vein systems in the central and northern portions of the Tonopah Mining District. The Seibert Formation is host to slightly younger, high-level epithermal, gold-bearing stockworks and breccias southwest and south of the Tonopah District at Three Hills, Divide, and Hasbrouck Mountain, with additional minor occurrences to the north.
Intrusions and flow-domes
The West End Rhyolite and Extension Breccia are coeval lithologies emplaced as sills along the gently west-dipping Tonopah Fault. The West End Rhyolite is a light green, fine to medium grained, "crowded" quartz porphyry rhyolite. Wilkins (1986) refers to the West End Rhyolite as "a typical Climax-type moly rhyolite". The Extension Breccia is a red, coarse grained autobreccia developed adjacent to, and during intrusion of, the West End Rhyolite. Both intrusive units were emplaced along the lower portions of the Tonopah Fault while Tonopah-type quartz-adularia-sericite veins were forming along the upper portions of the same low-angle fault. Both units appear to be differentiated, up-dip extensions from a deeply buried molybdenum porphyry west of Tonopah (Wilkins, 1986).
Oddie Rhyolite dikes and sills, common throughout the Tonopah Mining District, consist of pink to grey, porphyritic rhyolite. Oddie domes and flow-domes occur wherever Siebert Tuff has been preserved, especially in the southern Tonopah District and adjacent Divide District. Banding, brecciation, and marginal alteration and mineralization are common features of the Oddie Rhyolite domes. Brougher Rhyolites are younger than Oddie rhyolites, and are banded, grey to light brown, and porphyritic. Brougher domes occur throughout the Tonopah and Divide districts, but are usually not brecciated or associated with alteration or mineralization.
Fault geometry and timing was crucial to Tonopah-type quartz-adularia-sericite vein emplacement. The Tonopah Fault is concave-down, is elongate east-west, and dips gently west. The West End Rhyolite and Extension Breccia intrude the deeper, western portions of the Tonopah Fault. The central Tonopah veins developed during the rhyolite breccia intrusion along the up-dip, eastern portions of the Tonopah Fault and in steep fractures in the hangingwall of the Tonopah Fault. The steep veins generally strike parallel to the east-west long axis of the Tonopah Fault, in the hangingwall of, and normal to, the concave-downward plane of the Tonopah Fault. The steep veins were higher grade but seldom more than five feet wide. Stope widths (thicknesses) up to 40 feet were encountered along the gently-dipping Tonopah Fault in the central Tonopah District.
Similar structural geometry is indicated for the northern Tonopah District. The King Tonopah vein fills a near-vertical fault striking east-west. Other east-west veins and stringer veinlet zones occur in the King Tonopah workings and nearby drill holes, all indicative of an underlying low-angle, west-dipping, concave-down fault beneath the Northern Tonopah district similar in geometry to the Tonopah Fault.
Post-vein faults offset the steep east-west veins and the gentle west-dipping veins of the central Tonopah District. The most prominent post-mineral fault in the central District is the Halifax fault, a north-northwest to northwest striking, moderately east-dipping normal faults. The Halifax Fault offsets the eastern extensions of the Tonopah Fault in the central Tonopah District, dropping the associated veins down several hundred feet to the east. Houston's eastern Tonopah District drilling program encountered Tonopah-style veins and grades at depth in the hangingwall of the Halifax fault (F. Saunders, personal communication).
In the northern Tonopah District, several post-mineral faults offset the King Tonopah vein system. One or more early, steep northeast-striking faults offset the west side of the King Tonopah vein. The northwest-striking, moderately northeast dipping Halifax Fault was encountered at the east end of the King Tonopah's 300-level drift. The King Tonopah workings also expose relatively young, normal faults striking north and dipping steeply west.
Hydrothermal alteration of Mizpah andesites is concentrically zoned in the vicinity of Tonopah-type veins. A potassium-silica flooded zone may be as wide as twenty feet immediately around the vein, followed by an argillic zone up to 100 feet wide consisting of an inner zone of kaolin-halloysite with minor quartz and an outer argillic zone of montmorillonite with minor kaolin and sericite. The outermost alteration zone associated with specific vein formation is a greenish-grey propylitic assemblage consisting of calcite-sericite replacing albitized plagioclase, chlorite-rutile-pyrite replacing biotite, and chlorite-albite-calcite-orthoclase replacing the groundmass.
Alteration of the Tonopah Rhyolite units is a more silicic counterpart to the Mizpah alteration assemblage. Critical to exploration is recognition of thin quartz-adularia-chlorite veinlets in propylitized rock within 300 feet of Tonopah-type veins. Of equal exploration importance is the observation that mineralized, Tonopah-type quartz-adularia-sericite veins terminate upwards into quartz-calcite-pyrite stringer zones "containing little or no silver or gold". Propylitic alteration extends 600 feet vertically above vein tops (Bonham and Garside, 1979, page 111).
The predominant assemblage of hypogene ore minerals in Tonopah-type veins is chalcopyrite-galena-sphalerite-argentite-polybasite-pyrargyrite-pyrite-wolframite-electrum. Some of these minerals will occur in better-developed stringer zones immediately above or close beside vein lodes.
Fresh rock trace element geochemistry of Tonopah-type hypogene alteration and mineralization has not been compiled to date. Outcrop geochemistry of the region was compiled by Bonham & Garside (1982) but is of little value in evaluating and comparing drill results.
Abundant metallic refuse has been scattered over the northern Tonopah landscape during the last 100 years, creating potential impediments to geophysical investigations. Looking for silicic veins with EM-resistivity gear will also be impeded by the numerous, pyrite-bearing, silicic, Oddie dikes and sills intruding faults and fractures throughout the district. Geophysical funds are probably better spent on drilling or geochemistry in this case.
Bonham, H.F. and L.J. Garside, 1979, Geology of the Tonopah, Lone Mountain, Klondike, and North Mudlake quadrangles: Nevada Bureau of Mines and Geology Bulletin 92, 142 pages, 2 plates.
Bonham, H.F. and L.J. Garside, 1982, Geochemistry of the Tonopah, Lone Mountain, Klondike, and North Mudlake quadrangles: Nevada Bureau of Mines and Geology Bulletin 96, 68 pages, 5 appendices, 1 plate.
Nolan, T.B., 1935, Underground geology of the Tonopah mining district, Nevada: Nevada University Bulletin 29, no. 5.