Finding a Thesis: The Northern Route onto Mineral Ridge and a Little Geology

Heading north out of Silver Peak, with The Crater in view.

After checking out the southern route to Mineral Ridge while on my 1976 thesis quest, I headed north out of Silver Peak on then Highway 47 (now S.R. 265), carefully measuring the miles to the left-hand turnoff. This time, the road was exactly where the map said it would be, and it was a fairly good, bladed dirt road. And, if you remember from my last post in this series, I was on my way to the Mary Mine. Today, the Mary and nearby Drinkwater Mines are often combined together as one agglomeration known as the Mary-Drinkwater Mine or complex, and both are part of Scorpio Gold Corp's Mineral Ridge project, which has been in production since 2011.

Mineral Ridge on a portion of the Silver Peak 15' quad, courtesy USGS.

The road I took is the double-dashed track going west from old Highway 47 about a quarter mile south of The Crater. As can possibly be gleaned through past explorations of double-dashed roads in my ’72 Opel back in ’76, on older maps, especially ones dating significantly before the time of the exploration, these roads might have been anything from great, graded gravel roads to terrible two-track roads that were barely visible through overgrown sagebrush. I was fortunate this time, or so I thought as I turned west.

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And now, I'll go into the geology of Mineral Ridge just a little, as per my memory from work done there in the mid-late 1980s and published work available online or in journals I have on hand.

We are at the road junction, looking to the southwest.

We can see quite a bit from this viewpoint, notably the Mineral Ridge detachment fault and the Mary-Drinkwater Mine, labeled M-D Mine.

The Mineral Ridge detachment fault, in bright red above, places mostly Cambrian sedimentary rocks of the upper plate over the Precambrian to Cambrian Reed Dolomite, the Precambrian Wyman Formation, and early Tertiary-aged alaskite and granite of the lower plate (Noland et al., 2015). The details may be somewhat complex.

Two notes worth mentioning: 1) I've labeled the seds of the upper plate as "ЄpЄ" because although the upper plate rocks are dominantly Cambrian, there may be some late Precambrian rocks in one area, and 2) The Reed Dolomite is often shown as straddling the Precambrian-Cambrian boundary, but it is sometimes assigned exclusively to either the Precambrian or Cambrian. I'm treating it here as ЄpЄ.

The low-angle fault shown in dark-red above—it’s somewhat left of center—places tilted dark rocks, presumably of the upper plate, over seemingly less tilted or nearly flat-lying, orangey Reed Dolomite. The Reed is usually placed in the lower plate of the detachment (as it is here), but rarely, as in this article, it is placed in the upper plate. I place it in the lower plate or treat it as its own structural plate, as in this abstract, which unfortunately cannot be read online without some rigamarole (or maybe can't be read at all).

The Reed Dolomite is very thin on Mineral Ridge, it’s possibly attenuated, and it often looks microbrecciated. Although not obviously ductiley deformed, carbonates such as the Reed can be ductiley deformed and not show it: they can heal and recrystallize as fast deformation can occur, making ductile fabrics—if any formed—difficult to identify.

I’ve marked this probable detachment surface—in the labeled photos above and below—in dark red, to contrast with the bright red of what I know to be the Mineral Ridge detachment fault.

Here's a closer view of that low-angle surface. It's probably a continuation of the Mineral Ridge detachment fault, only lower in elevation and closer to us.

I've labeled the known upper plate (UP) and lower plate (LP) rocks. The ?? in bright red is probably upper plate.

I'm only saying that the dark-colored rocks of these photos are "probably" upper plate because I haven't personally walked this ground, unlike many other sections of ground on Mineral Ridge. They are shown as shown as Cambrian limestone and dolomite undivided here, with the fault being the Mineral Ridge detachment fault.

Because from a distance the tilted dark-colored rocks look to me like Tertiary volcanic rocks, I'll add another side note: A small hill of Tv occurs south of the Oromonte and Wedge Mines (south to SSW of the Mary-Drinkwater complex). When I mapped in the area, I wondered if the reddish volcanic unit exposed on that small hill was tilted as part of the upper plate, or untilted as part of a younger unit erupted after detachment faulting ceased. I don’t really remember my conclusion. On this map (Diamond and Ingersoll, 2003, p. 464), the Tv is post-detachment and lying on top of Te (Tertiary Esmeralda Formation), which I recall as being tilted (the Te is in the upper plate of the detachment fault, whereas the Tv overlaps the detachment fault and therefore post-dates it).

Aaaand, back to 1976:

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Onward I drive: up the coalesced alluvial fans emanating from New York, Echo, and Eagle Canyons, Custer and Great Gulches, and other lesser gulches and canyons. I was finally on the northern approach to the Mary Mine and the top of Mineral Ridge.

The road in 2010. It's unlikely that power lines paralleled the road in 1976.

Woh! Suddenly the road ends in a huge washout.

But in 2010, the accessible part of the road ended like this.

Locked gates are the way of the mining world.

I have some things to say about locked gates, but I’ll save them for another post.

Still in the Opel, I carefully meander up the sandy dry wash until I come right up against a 50-foot-high wall of dirt and rock: Instead of a road, I’m looking at a filled-in canyon between two cliffy ledges. I know the road continues on, somewhere beyond this pile of debris, but I can't get to it! I walk around, searching unsuccessfully for a go-around or bladed connection between the washed-out road and the rest of the road.

Resigned to hiking, I park in the sand wash, carefully pointing the car downhill for a quick getaway; I get my field gear and maps out of my car and start walking up the hill toward the Mary and Drinkwater Mines.

To be continued...

Selected References:
Albers, J.P., and Stewart, J.H, 1972, Geology and mineral deposits of Esmeralda County, Nevada [available for sale only]: NBMG Bulletin 78, 80 p.

Diamond, D.S., and Ingersoll, R.V., 2002, Structural and sedimentologic evolution of a Miocene supradetachment basin, Silver Peak Range and adjacent areas, west-central Nevada, in The George A. Thompson Volume: The Lithosphere of Western North America and Its Geophysical Characterization: International Geology Review, p. 588-623.

Hulen, J.B., 2008, Geology and Conceptual Modeling of theSilver Peak Geothermal Prospect,Esmeralda County, Nevada: unpublished report for Sierra Geothermal Power Corporation, 23p.

Noland, P.D., Briscoe, Scott, and Hawley, P.J., 2015, Genesis and Timing of Gold Mineralization at Mineral Ridge, Esmeralda County, Nevada, and Implications for Future Exploration and Discovery [entire article], in New Concepts and Discoveries, GSN 2015 Symposium Proceedings: Geological Society of Nevada, p. 153-168.

Powers, S.L., 1988, Two lineation directions in the Mineral Ridge core complex, Esmeralda County, Nevada [abs, not available]: Geological Society of America, Abstracts with Programs, v. 22, no. 3, p. 222.

Spurr, J.E., 1906, Ore Deposits of the Silver Peak Quadrangle, Nevada: U.S. Geological Survey Professional Paper 55, 174 p.

Wesnousky, S.G., 1994, Evaluation of the geologic relations and seismotectonic stability of the Yucca Mountain area, Nevada Nuclear Waste Site Investigation (NNWSI), Progress Report 30 September 1994: UNR, Mackay School of Mines, Center for Neotectonic Studies. Accessed via NRC website.

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