Montgomery Mine

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From Mines and Mineral Deposits in Death Valley National Monument, California, 1976:

Ownership: Cyprus Industrial Minerals Company.

The Montgomery mine, the most westerly of the talc mines in the Death Valley region, is high on the ridge that separates Warm Spring and Galena Canyons. This deposit is one of the rare occurances of silicated rock that is associated with a cross-cutting body of diabase rather than a sill. Because most of the diabase bodies crosscut dolomite of the Crystal Spring Formation, the talc occurs in displaced blocks within a fairly uniform zone.

The margin of the diabase dike strikes eastward and is bordered on the north by carbonate rocks of the Crystal Spring Formation. Here, as elsewhere, the zone of silication that contains the bodies of commercial talc is altered lower strata of the carbonate member, but it forms a lens that strikes northwest at an angle of about 30° with the diabase contact and thins and daylights to the north.

At this locality, the zone of silicated rock averages a fen tens of feet in thickness and is about 500 feet in exposed length, strikes northwest and dips about 20° to 30° southwest. The talc of commercial interest occurs in two layers, the lowest of which has been the most extensively mined. The layers are separated by beds of darker-colored silicate-carbonate rock. Also bordering the margin of the diabase body, but higher in the carbonate member, are layers of green tremolite rock oriented parallel with the strata. The two principal layers of talc are from about 10 to 15 feet in thickness and are separated by 8 to 12 or more feet of the darker rock. The talc is generally blocky but crudely foliated and tinted grey to green.

The lower layer was mined underground prior to 1972, primarily during the 1940s; but work in the fractured, caving ground had to be discontinued. Hazardous mining conditions requiring extensive timbering, coupled with a recovery rate of 35 percent, required development of the talc through surface mining.

Since 1973, a pit has been in development. Overlying waste rock from the southeast-dipping talc beds was being removed according to plan. Stripping ratio is 13 to 1. About 688,000 tons of overburden were removed in 1974, about 281,000 in 1975. The company plans to remove between 200,000 and 300,000 tons during 1976. Depth of the final pit will be approximately 300 feet on the southeastern wall, and it will be open on the northwest end. Maximum pit perimenter will be approximately 850 by 850 feet. Map 6 shows the final pit plan and a cross-section drawn through the pit. Waste is removed by one D-9 bulldozer, one 7-yard front-end loader, and one 35-ton-capacity truck. The talc layer is easily ripped and usually loaded by a 3-yard-capacity front-end loader on a 10-ton-capacity truck for transportation to the stockpile, which is downslope to the west. The larger equipment is sometimes used for mining. Material is taken by contract truckers to the mill at Los Angeles or Dunn Siding for direct shipment to mills in Grand Island, Nebraska, and Mexico.