M. G. L. Mine, Nightingale Mining District, Pershing County, Nevada, USAi

Regional Level Types
M. G. L. Mine	Mine
Nightingale Mining District	Mining District
Pershing County	County
Nevada	State
USA	Country

Sec 15 T25N R24E
Structure: Post Mineral Faults

Alteration: Silication And Silicification

Deposit: At several places 0.5 to 1.0 mile east of the m. G. L. Mine, scheelite is found in small tactite inclusions in granodiorite within a fe W hundred feet of the main mass of sedimentary rocks. These inclusions are all shallow, As indicated by diamond drilling by the m.g.l. Mining corp., and contained only a few hundred tons each of mineable ore, most of this ore w-as probably mined during the 1953-1956 period. ; info.src : 1 pub lit; 2 unpub rept; 3 field observ six principal orebodies were mined. The largest was in that south rotated block of limestone. At the surface, this block was surrounded by highly quartzose tactite, 5-20 ft thick, consisting of 70-90 % quartz and 10-30 % epidote, pyroxene, hornblende and garnet with small quantities of sulfides. Between this -layer and the central core of marble was a band of scheelite-bearing tactite on the south, west, and north sides of the block. In depth, the scheelite-bearing tactite thickened at the ex-pense of the marble and about 100 ft beneath the outcrop, the -marble was replaced by ore across the full width. At 150 ft, t-he ore was cut off by granodiorite. The ore mined contained 0.-75 to 1.0 % wo3. Other smaller orebodies to the north also consisted of rims of tactite about 5 ft wide around cores of marble, separated from each other by tongues of granodiorite. Contact zone is between a thick sequence of argillaceous and calcareous sedimentary rocks and an intrusive body of granodiorite. The contact is nearly conformable but the contact zone is intricately injected by granodiorite, resulting in -mixed rocks. The central part of the contact zone consists of a band of limestone about 80 ft wide, partially altered to tactite. The rocks on either side are hornfels or schist, mixed with granodiorite. At depths of a fe W hundred feet, the granodi-orite cuts across the sedimentary rocks and cuts off the favorable limestone beds. In most of the contact zone, bedding is parallel to that in the main mass of sedimentary rocks to the Southwest. However, at the south end of the mine, an irregular block of limestone about 80 ft wide and 120 ft long, entirely surrounded by granodiorite at the surface, has been rotated 45 degrees. This block apparently floated As an inclusion in the granodiorite and not only rotated, but also moved 100 ft sw.

Deposit type: W skarn

Development: Small amount of ore produced in 1917-18. From 1942-45 the mine was operated by the m.g.l. Mining corp which built a 100-ton flotation concentrator. The mine was reopened during 1952-56 and worked by various lessees. It has been idle since 1956.first production in 1918 by c. R. Cowles and associates, who mined about 80 tons that averaged 1.28 % wo3. The pro-perty was acquired by the m.g.l. Mining corp. In 1941 and a mi-ll was built at the mouth of cowles canyon. Most of the production was during world war ii (1942-1945). A small production was reported in 1953-56 and included several hundred units from- reworked tailings. Recently overstaked(?)(1985) before the mine was closed in 1945, the operators drilled 82 diamond drill holes to explore tme area and delineate the ore bodies. This exploration did not discover any additional orebodies that could be mined profitably in 1945.

Geology: Areas of schist and slate are invaded by granodiorite tongues parallel to bedding. Limestone (marble and hornfels) are cut into irregular-shaped blocks by granodiorite dikes. Scheelite seen is pure white and less than a 1/4 inch thick. Deposits carry considerable garnet in contrast to deposits on eastern slope of nightingale range. W deposits in tactites at limestone/granodiorite contact. Scheelite concentration vary in alternating layers.

Rock formation(s): Auld Lang Syne Group


Ore(s): Igneous Contact

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Link to USGS MRDS:	10042417

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References