Homestake Mining Company -- McLaughlin Mine
Geology of the McLaughlin Deposit
By Dean Enderlin, 2002

Geology of the McLaughlin Deposit continued . . . Page 4 of 5

Minerals of McLaughlin
The variety of minerals found at the McLaughlin mine is well known and extensive. A small sampling is presented below.
Lemon Opal

A form of common opal (no fire), this opal was found at the surface in only one spot in the McLaughlin deposit. The deep yellow pigment was due to hydrocarbon impurities (probably curtisite), which also made the lemon opal fluoresce under UV light. D. Enderlin photo.

   
Precious Opal

In spite of the abundance of opal throughout the McLaughlin deposit, only one small pocket of precious opal was ever found. The samples at right display green and orange fire. N. Lehrman photo.

   
Mercury and Cinnabar

Cinnabar is the red sulfide of mercury. The image at left shows the liquid metal (mercury or quicksilver) with a piece of cinnabar from the old Gail Pit. Cinnabar was widespread in the shallow portions of the deposit, but was rarely seen as the pit was deepened. D. Enderlin photo.

   
Metacinnabar

At one time, it was thought that these black banded veins were the barium-manganese oxide, psilomelane. Later study revealed that they were composed of metacinnabar, a close "cousin" to cinnabar.  The sample at right comes from San Quentin Hill. D. Enderlin scan.

   
Cinnabar

Cinnabar in the McLaughlin deposit often appeared as earthy replacements or as small crystals. The sample at right was collected from the Zodiac Sill in the North Pit. The crystals in this pocket were exceptionally coarse. This pocket also contained native mercury, which was extremely rare at McLaughlin. D. Enderlin photo.

   
Myrickite

Named for the famous Death Valley gemstone prospector, "Shady" Myrick, Myrickite is one of the more spectacular gemstones found in the McLaughlin deposit. Its alternating black and red-orange bands are metacinnabar and cinnabar, respectively, which are silicified by opal and chalcedony. D. Enderlin photo.

   
Myrickite

Normal cinnabar is soft and not suitable for jewelry making. Myrickite, on the other hand, is hard enough to take a high polish. It was much sought after by rock collectors. Unfortunately, there was only one outcrop west of the McLaughlin open pit that yielded the best Myrickite. The seam was excavated prior to gold mining operations, and the best material provided to a gem dealer for sale on consignment. D. Enderlin photo.

   
Myrickite

The specimen of myrickite at left has been polished to reveal the intricate color banding that makes it so desirable. D. Enderlin scan.

   
Stibnite

Antimony minerals are relatively common in McLaughlin mine ore. Stibnite (antimony sulfide) is the most common of all the antimony minerals at McLaughlin. It usually occurs as thin silver metallic needle-like crystals in the siliceous veins. The specimen at right came from one of the better stibnite pockets found at McLaughlin, located at the north end of the South Pit. D. Enderlin photo.

   
Stibnite

The stibnite sample at left is more typical of crystals found at McLaughlin. The "spray" of crystals measures about an inch in diameter. D. Enderlin photo.

   
Pyrite (Fool's Gold)

Pyrite was widespread in the McLaughlin deposit, but generally not coarse-grained. The crystal cluster shown at right (with a vial of Mother Lode placer gold for comparison), came from an altered zone in sheared Knoxville mudstone. Such shear zones occasionally yielded pockets rich in beautiful large pyritohedrons such as this one. D. Enderlin photo.

Animated globe courtesy NOAA NESDIS National Geophysical Data Center 
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