Western Nevada starts to catch the wave

Even though it is sometimes in the shadow of the “big trends” like Carlin or Battle Mountain, Nevada’s Walker Lane trend is the home of many of the Silver State’s legendary mines — Tonopah, Goldfields, the Comstock Lode — and a very different metallogenic environment with very different exploration targets.

Where the trends in northern Nevada are linked to thrust and extensional faults, the Walker Lane — which flanks the Sierra Nevada in the western part of the state — has been described as a long, wide shear zone or system of strike-slip faults. And having been much more a centre of magmatic activity than its northern counterparts, gold deposits in the Walker Lane occur preferentially in the volcanic rocks, rather than in the sedimentary rocks.

Competent volcanic rocks typically fracture, rather than flow, so epithermal precious metal deposits form stockworks or vein systems. So rises the accepted model of a Walker Lane gold deposit: narrow veins with bonanza grades.

In the 1980s, big, low-grade gold deposits were popular and heap leaching was the way of the future, which imposed another model on the deposits of the Walker Lane: narrow veins with bonanza grades averaged over a big open pit. Bullfrog, Aurora and Round Mountain displaced Goldfield and Tonopah in explorers’ dreams.

Then the cold days of the late 1990s arrived and the only dream Nevada explorers had was of higher gold prices. When the higher prices arrived, explorers came back, but the noise was made along the Battle Mountain trend, with discoveries like Cortez.

In the quiet to the west, exploration companies are getting results by concentrating on the kind of deposits the Walker Lane does best. Fortunately, in the present climate, you don’t need one of Nevada’s tonier addresses to raise money, so most explorers in the trend have cash to do their work.

Pine Grove

Romarco Minerals (R-V, RTRAF-O) has completed an initial phase of drilling at the Pine Grove project, in Lyon Cty., 37 km south of Yerington. Four deep reverse-circulation (RC) holes tested two targets on the property, one a set of outcropping veins and the other a target that had been drilled in the 1990s by Inmet Mining (IMN-T, IEMMF-O).

One hole intersected the downdip extension of the outcropping veins at about 250 metres down-hole, cutting 3 metres grading 1.3 grams gold per tonne. Another intersection, about 35 metres further down-hole, cut 3 metres grading 0.65 gram per tonne. A second hole on the same target intersected the veins at depth, but the gold grade of the intersection only ran 0.15 gram per tonne.

On the old Inmet target, one hole encountered an average 0.96 gram per tonne over 110 metres, with individual 3-metre intersections running as high as 5 grams gold per tonne. Eight 1.5-metre intervals in the hole assayed higher than 2 grams per tonne.

More drilling is planned in the summer season, including tests of targets around the old Rockland mine, which produced 35,000 oz. gold in a 60-year career of sporadic production — at gold grades around 2.6 oz. per ton (89 grams per tonne). Romarco is earning a 60% interest in the property from privately owned Toquima Minerals by spending US$2 million on exploration work by the end of 2009. It can bump that interest another 10% by providing a final feasibility report.

Monte Cristo

At the Monte Cristo property about 70 km northwest of Tonopah, Gold Summit (GSM-T, GDSJF-O) is currently reviewing an outside consultant’s resource estimate. Reno, Nev.-based Mine Development Associates put the inferred resource on the McLean Lode deposit at 331,000 tonnes grading 6.5 grams gold and 20.6 grams silver per tonne, using a combined silver-gold cutoff grade equivalent to 3.4 grams gold per tonne. The calculation is based on 197 drill holes by Gold Summit and earlier operators.

The consultants identified three domains in the deposit: two lower-grade domains called the Lode and Low Grade domains, and a higher-grade Vein domain where 189 samples showed an average grade of 8.4 grams gold per tonne, with the highest-grade sample topping out at 253.6 grams gold per tonne.

In October, Gold Summit drilled a hole near the northeast edge of the McLean pit, a 1980s-vintage open pit that fed a small heap-leach operation. The hole, at depth, cut 1.3 metres grading 12.1 grams gold and 119 grams silver per tonne. At 240 metres down-hole, it was the deepest intersection yet on the target.

Drilling immediately west of the pit in 2005 intersected 1.2 metres grading 14.6 grams gold and 1,309 grams silver per tonne.

Fletcher Junction

Reno-based Battle Mountain Gold Exploration (BMGX-O) is doing a more grassroots project at Fletcher Junction, in Lyon Cty., about 8 km north of the Aurora mine. Battle Mountain (no relation to the old producer) staked the area based on the results of groundwater prospecting for gold. The technique rests on migration of gold and associated trace elements — silver, arsenic, antimony, and base metals, all of which occur in the mineralization — from oxidizing gold deposits into the groundwater system.

Battle Mountain ran a sampling program in 2004, finding anomalous concentrations of gold in groundwater in the Fletcher Junction area. As an added attraction, the northwest-striking faults that control the mineralization at Aurora appear to extend, beneath cover, to the Fletcher Junction area. The property awaits drilling.

Borealis

A short distance away in Mineral Cty., Gryphon Gold (GGN-T, GYPH-O) is working on mine-site exploration targets at the Borealis mine. Borealis, which produced about 635,000 oz. for Tenneco Resources and Echo Bay Mines in the ’80s, still has an indicated resource of 40.5 million tonnes grading 1 gram gold per tonne and an inferred resource of 31.5 million tonnes running 0.7 gram.

Gryphon picked up Borealis from Golden Phoenix Minerals (GPXM-O), which had taken the property on in the late 1990s. A 2002 joint venture turned into an outright purchase in 2005, as Phoenix concentrated on the Mineral Ridge property in Esmeralda Cty., where it is re-leaching the existing heaps.

At Borealis, Gryphon’s strategy has been to drill both structural extensions of the known mineralization and geophysical anomalies identified in induced-polarization (IP) surveys.

RC drilling on extensions to the known resource has returned some long intersections, particularly in the area of the old Freedom Flats pit, where a 74.7-metre intersection averaged 1.9 grams gold and 15 grams silver per tonne, including a 10.7-metre interval that ran 6.5 grams gold.

Two outside targets, both with IP anomalies on them, have also cut some mineralization near the resource grade over significant widths. Two holes on the Middle Ridge target cut 44 metres grading 0.7 gram gold and 1 gram silver per tonne, and 41 metres grading 0.9 gram gold and 3.1 grams silver per tonne.

Two others, on the Graben target, cut 26 metres that averaged 2.4 grams gold and 10.2 grams silver and 76 metres that averaged 2.1 grams gold and 8.9 grams silver.

Farther to the southeast, in Esmeralda Cty., Golden Odyssey Mining (GOE-V, GODYF-O) has sampled on the Palmetto project, about 50 km southwest of Goldfield. Golden Odyssey’s thinking is that the property — long held by a hobby-miner and mostly unsullied by modern exploration — may host a skarn or porphyry-gold deposit.

The company’s choice has been rock-chip geochemistry, which has identified four target areas showing copper grades of 1.9% to 11.6%, with associated trace levels of gold, silver, mercury, molybdenum, antimony and arsenic.