Outcropping reduced intrusion related gold system
Located in Nevada
The Buffalo Canyon property includes the recently recognized Oligocene reduced intrusion gold system called the Everson Deposit. Forty-seven reverse circulation drill holes completed by four companies between 1992 and 2017 have partly defined a zone of gold mineralization within a surface area with dimensions of 500 by 600 meters (approximately 1640 by 1970 feet. All holes intersected long intervals of anomalous material except for two drilled off the range front that did not reach bedrock. Preliminary cyanide leach analyses indicate the likelihood of favorable metallurgy.
The Buffalo Canyon property lies within the Union Mining District in northwestern Nye County, Nevada approximately 120 kilometers (75 miles) southeast of Fallon, and 4 to 7 kilometers (2 to 4 miles) south of the town of Ione.
The Buffalo Canyon Project adjoins the historic mining camps of Berlin and Ione in the Union Mining District where high-grade mesothermal quartz veins and quartz--adularia veins were mined for gold and silver in the 19th and 20th centuries. Past production at the Berlin Mine, approximately 40,000 ounces of gold came from mesothermal bull quartz veins mined with underground methods.
Modern exploration of the area began in 1992, when Gold Fields Mining Corp., with the use of a regional stream sediment sampling survey, discovered gold mineralization along the western flank of the Shoshone Range. Follow-up rock chip sampling and mapping identified the stockwork vein mineralization, then known as the Rich Dude prospect. Gold Fields drilled 5 holes, four of-which intersected significant gold mineralization ranging from 0.582 to 0.925 g/tonne (0.017-0.027 oz/ton). Santa Fe Pacific Gold, subsequently, acquired the property in 1993, completed a grid soil survey, and drilled 12 holes in the Rich Dude area, all of which intersected zones of gold mineralization exceeding 0.4 g/tonne (>0.012 oz/ton). In 2002, Nevada Pacific Gold re-staked the property and completed additional geologic mapping and rock chip sampling. In 2005, they drilled 23 holes, confirming the style and grade of mineralization in 16 of the holes. Subsequently, U.S. Gold, now McEwen Mining, acquired Nevada Pacific's interest in the prospect by means of a merger, but conducted little additional field work and allowed their claims to lapse in September 2012.
Of the holes completed in the three historic campaigns, half intersected more than (30 meters) 100 feet of mineralization averaging more than 0.342 g/tonne (0.010 oz/ton) gold at a cutoff of 0.171 g/tonne (0.005 oz/ton). Eleven holes penetrated mineralized bedrock at the surface and thirteen ended in mineralization at depths of 152 meters (500 feet) or more. Importantly, cyanide shake recoveries average approximately 75% in unoxidized material obtained from drill holes. This is typical of reduced intrusion gold systems and what makes them a viable gold deposit type worldwide.
In late 2002, AuEx Ventures, Inc., the predecessor of Renaissance Gold, staked a large claim block north, east, and southeast of the Rich Dude claims. Detailed mapping and sampling identified widespread gold mineralization associated with a variety of quartz vein styles (up to and exceeding 30 g/tonne, jasperoids (locally exceeding 1 g/tonne), and intrusions (locally exceeding 1 g/tonne). In 2008, a joint venture agreement was reached with Eldorado Gold, who subsequently completed additional mapping and sampling, a detailed soil survey, and a detailed ground magnetic survey. After obtaining Forest Service approval, 18 holes were drilled in 2011 to test a variety of targets, including jasperoids, orogenic quartz veins, and sheeted quartz veins. Several of the better intercepts are mentioned in the "Geology" section of this summary. Eldorado Gold terminated their interest in 2012, prior to the acquisition of new ground covering the Rich Dude zone of mineralization in the western portion of the property.
In 2017 Patrick Quillen completed a master’s thesis on the project identifying the system as Oligocene in age.
The project area is underlain by siliciclastic, volcaniclastic, and volcanic rocks and minor limestones of the Triassic-aged Knickerbocker Formation. These rocks have been intruded by a series of stocks and dikes of porphyrytic to equigranular diorite, quartz diorite, and granodiorite of undetermined age. Broad zones of biotite and pyrrhotite-bearing hornfels have formed around the intrusions, and magnetite skarns have locally formed adjacent to intrusive contacts.
Gold is associated with most of the intrusions in the project area, although the style of alteration and mineralization varies, partly in-response to the oxidation state of the intrusions. A reduced oxidation-state stock at the Everson area is associated with at least two stages of stockwork to sheeted veins. Both vein stages are gold-bearing, but the latter stage appears responsible for the majority of gold mineralization identified to date. In addition to gold, the veins are strongly anomalous in bismuth and moderately anomalous in copper. Drilling indicates that gold mineralization is open-ended at depth, and occurs at a number of locations within the pyrrhotite annulus.
Approximately 1 kilometer (0.62 miles) to the northeast of the Rich Dude stock, a small diorite plug is associated with tourmaline breccias, tourmaline veins, and base metal veins whose mineralogy includes pyrrhotite, sphalerite, and arsenopyrite. Soil sampling has documented a 1-kilometer-diameter (0.62 miles) zone of strong lead and zinc enrichment, with a centrally located zone of anomalous arsenic and copper.
In 2011, near the north end of the property, previously unmapped gold-bearing jasperoids yielded drill intercepts that included 7.6 meters (25 feet) of 0.685 g/tonne (0.020 oz/ton) and 10.6 meters (35 feet) of 0.616 g/tonne (0.018 oz/ton) gold. These jasperoids may be related to a concealed dike-shaped, magnetite-bearing, intermediate-composition intrusion intercepted by drilling, or they could be distally related to the reduced-oxidation-state intrusions located 1 to 3 kilometers (0.62 to 1 miles) to the south.
In the southern portion of the property known as the "South Doonan" area, a small granodiorite stock lies near a sheeted and banded gold-bearing quartz vein swarm at least 350 meters (1150 feet) long that contains pyrite and local stibnite. The only two drill holes that have tested this zone intercepted 15 meters (50 feet) of 0.411 g/tonne (0.012 oz/ton) Au and 7.6 meters (25 feet) of 0.514 g/tonne (0.015 oz/ton) Au, respectively, in 2011.
Mesothermal-style, gold and base-metal-bearing, bull quartz veins occur in a broad, 2 km2 (0.77 mi2) area distal to gold-bearing stockwork and sheeted veins associated with reduced intrusions at the Everson and, possibly, the South Doonan areas. The bull quartz veins contain minor amounts of base metal sulfides (pyrite, galena, sphalerite, chalcopyrite) and local visible gold and have yielded surface rock chip assays of up to 17.9 g/tonne (0.522 oz/ton) gold. The possible distal relationship of these veins with the intrusion-related stockwork mineralization is consistent with observations from other reduced oxidation-state granitic intrusions (Thompson and Newberry, 2000), where the bulk of gold reserves are contained in the more proximal quartz vein stockworks. This underscores the potential for bulk-tonnage gold resources at depth, particularly in the Everson area, where mineralization appears to continue at depth and southward, projecting beneath surface outcrops of gold-bearing bull quartz veins.
Deposit Description: Mineralization styles at the Buffalo Canyon property include: 1) stockwork and sheeted gold-bearing quartz-tourmaline and quartz-actinolite-albite veins proximal to reduced oxidation-state intrusions (Figure 3), 2) mesothermal gold and base metal-bearing bull quartz veins distal to reduced oxidation-state intrusions, and 3) gold-bearing jasperoid within carbonate units, whose relationship to reduced or oxidized intrusions remains unclear. Of these styles, the stockwork veins of the Everson Deposit proximal to reduced intrusions comprise the most significant targets identified to date.
The gold-bearing stockwork vein system of the Everson Deposit cuts several phases of the mapped intrusive complex and adjoining meta-sedimentary and meta-volcanic country rocks. The intrusive complex lies within a biotite-pyrrhotite halo documented in surface mapping and a detailed ground magnetic survey. Most of the halo has not been drilled, but strongly anomalous rock chip and soil samples indicate significant potential away from known mineralization. The cross-cutting stockwork vein system, seen in outcropping intrusions, suggests that a causative intrusion(s) could be concealed at depth. Importantly the drilling has not breached the carapace of such an underlying intrusion(s), where higher grade mineralization could occur as seen in similar systems such as Bald Mountain in Nevada or Ft. Knox in Alaska.