Sunday, February 24, 2008

Hmmm...

This month's Accretionary Wedge is up at Lounge of the Lab Lemming: Geohmms (Accretionary Wedge 6). He runs down the many interesting geological articles quite well.

One thing I wonder - is a particular kind of "blue quartz" really associated with ore deposits - ore deposits of the gold kind? Some have postulated this idea, at least informally: for example, here and here. A familiar example to me would be an unusual bluish quartz found in the Silver Peak Mining District, on top of Mineral Ridge, near Silver Peak, NV (the town, not the peak). I noticed blue quartz while working there long ago, especially in and around the old Gold Wedge and Oromonte claims above the Mary Mine. The quartz occurs in granitic rock, and I've seen it most commonly near the relatively flat-lying quartz veins or ledges of the area. It appears to be an alteration feature or late stage intrusive feature, though the granitic rocks are entirely within the lower plate of a core complex and are often mylonitized or mylonitic. The timing of quartz veining and the gold-mineralizing event is unclear, at least in the sense that the many mining companies that looked for gold there (in the 1970's to 1980's in particular) all seemed to use different deposit models, from Carlin-type to exhalite-type to some variation of Mesquite-type, and even, possibly, to some variation of Mother-Lode-type (mesothermal veins). At this juncture, it would be a good idea to show an example of the blue quartz. If I have any examples, they are packed in boxes in the garage from my last move in 2001. I haven't been to the top of Mineral Ridge since the day after New Year's Day in 2000 (a geo-millennial thing, I guess), and at that time, the entire area was fenced off from recently shut-down mining operations, operations which appeared to have placed a heap-leach pad over part of a gold deposit discovered in the late 1980's by Former Mining Company. From this Google Earth image, it looks like the best outcrop of blue quartz might be almost or entirely gone!

Silver Peak, by the way, is another "outback" Nevada town or village. It was the largest town in Esmeralda County in the mid-1980s when its population was about 1500 because of silver and lithium-brine mining, and the population of Goldfield, the county seat and only other town in Esmeralda County was a third of that or less.

Silver Peak is A Virtual Paradise.

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