The White Rock prospect is in northeastern Nevada in the Goose Creek Mountains along the Nevada – Utah border. Montello is the closest community to the prospect that provides lodging and meals.
The White Rock prospect was originally located by AMAX GOLD in 1984. By 1989 exploration drilling had reportedly indicated the presence of a large low-grade gold reserve. Original calculations of geologic reserves for the property by AMAX were 162,000 oz of 0.018 opt Au. Drilling by Kennecott has not appreciably changed these figures.
The terrane in the White Rock Area is composed of a Permian-age bedded sequence of limestone, chert, siliceous siltstone, and cherty limestone. These beds dip gently southward and are capped in places by the remnants of a Miocene-age rhyolitic flow. The Permian rocks within the 2-square-mile area of interest are chiefly siliceous siltstone beds which are tentatively correlated with the Rex Chert member of the Phosphoria formation. These beds are variably crackled, altered, and mineralized; the most intense effects are found bordering NNE trending fault zones.
A ~N20E striking fault system forms the boundaries of a large graben ¾ of a mile across.Permian sedimentary rocks are exposed in topographic highs on either side of the graben. Within the graben both Tertiary volcanic and Permian sedimentary rocks are exposed. A north-south striking fault system within the larger graben defines a horst that exposes Pz sedimentary rocks in the center, bounded by Tertiary volcanic rocks on the east and west.
Mappable alteration effects in the Rex siliceous siltstone include bleaching, silicification, quartz veining, iron oxide staining, and brecciation. Introduced alteration minerals include pervasive jarosite, hematite, limonite, and goethite and localized scorodite, apatite, alunite, kaolinite, and variscite. The Miocene volcanic rocks are generally unaltered and not mineralized, but some puzzling exceptions are found off the claim block to the southwest.
Low-level gold, arsenic, and mercury anomalies generally coincide with the outcrop pattern of the Rex Chert, with values increasing in the vicinity of fault zones. This mineralization presumably extends out beneath post-mineralization cover to the east, south, and west of the drilled area.To the north, the faults and associated mineralization appear to die out in the limestone beds of the Grandeur formation.
In outcrop samples a peak gold content of 15 ppm is reported. Arsenic values greater than 500 ppm and mercury contents greater than 1.0 ppm are common. The best 5 ft drill intercept is reportedly 0.07 opt gold.
Fault orientations and gross geochemical patterns of Au, As, and Hg suggest that mineralizing fluids moved up dip in the Rex Chert along faults and shear zones from an undrilled, covered, source area in the southwest portion of the claim block. This area therefore rates as a prime target for future exploration.
Comparison of prospect geology with drill hole locations and Au, As, and Hg distributions also suggests that previous drilling efforts mostly tested vertically beneath the structurally controlled surface geochemical anomalies. In several cases this drilling did not prospect the anomalies in the down-dip direction, nor was there any serious effort made to test below the post mineral cover that separates some of the gold anomalies.
Examples of these types of untested drill targets are; A. the westward side of the shallowly west dipping gold anomalous fault zone that passes through hill 7220 and, B. the north trending covered area at the northwest corner of section 5 which is bordered by gold anomalies.These and other quality targets remain to be tested at White Rock. The western zone is essentially untested. The attraction here is the occurrence of strongly anomalous geochemical gold values situated on the borders of a north trending graben. The continuity and grade of mineralization across the graben and evidence of any possible mineralization controls are obscured by a thin capping of Tertiary volcanic rock.
AMAX’s final drilling effort (DHs 45 – 51) was directed, in part toward testing the margins of the western graben.Unfortunately, the results of the program were, at best inconclusive due to drilling problems brought on by an inexperienced driller.Only two of the seven holes drilled reached their objective and only one of these had reasonable sample recovery. For instance, in DH-48 there was no sample recovered over a 50-ft interval which intriguingly is bordered by 1000 ppb Au assays.Additionally, the bottom 40 ft of this hole averages 337 ppb Au. Similarly, DH-49, the only hole collard within the graben cut a 100-ft intercept grading 0.019 opt Au which includes 40 ft @ 0.04 opt Au. The hole bottomed in 151 ppb Au. AMAX nevertheless had become disenchanted with White Rock and despite the inconclusive results abandoned it leaving several promising targets untested.
The Kennecott program did not attempt to offset the holes drilled by AMAX having better gold-grade intercepts, instead it seems to have been more of a reconnaissance effort, drilling remote targets ranging 470 – 1400 ft from the nearest AMAX hole.The program had mixed results in that; 3 of the holes were abandoned short of their objective (W-4, 6, and 8), four holes had discouraging results (W-1, 2, 5 and 9), and two holes (W-3 and 7), had results that clearly deserve follow up.
Kennecott hole W-3 in the western graben is the best mineralized hole drilled on the property thus far. One of the better intercepts in this hole is 60 ft grading 0.03 opt Au which includes 10 ft @ 0.116 opt Au. The hole has an aggregate gold-mineralized footage of 250 ft @ 0.02 Au opt.
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