Mina Tiro Estrella, Capitan Mining District, Capitan Mountains, Lincoln County, New Mexico, USAi

Regional Level Types
Mina Tiro Estrella	Mine
Capitan Mining District	Mining District
Capitan Mountains	Mountain Range
Lincoln County	County
New Mexico	State
USA	Country

The Mina Tiro Estrella quartz locality has long been famous for producing some of North America's finest Japan-law twins. What sets the twins apart from many other localities is their smoky color, gem quality, mirror-like luster and pronounced striations on the flattened crystal faces. The twins were first found by Dick Jones in 1976 when he reportedly followed the directions of a hunter that had stumbled across some quartz float, including some Japan-law twins, in the Capitan Mountains during a deer/elk hunt. Dick Jones located the place where the twins had been discovered and filed several claims in the area. The problem was he intentionally recorded the claims a half mile further than their actual physical location to protect the property from claim-jumpers, including the claim with the majority of the quartz mineralization, the “Mina Tiro Estrella”. This gave Dick a chance to dig on the Mina Tiro Estrella unhindered and resulted in a major strike in 1978-1979. Many twins of the best quality were found, several of which are pictured here. By 1980 the word was out and other collectors were able to locate the claim and high-grade some fine twins from the diggings. Dick let the claims lapse soon after, and although other people re-filed the claim, not much more significant material has been produced since this time.
NOTE: The Mina Tiro Estrella claim is currently under ownership and collecting is not allowed. Smokey quartzes similar to http://www.mindat.org/photo-224147.html are sometimes reported from this locality but are almost certainly from the nearby Smokey Bear prospect instead.

The Mina Tiro Estrella smoky quartz occurrence is hosted in a feldspar and quartz-rich granite called alaskite. The mineralization is present in the form of a brecciated vein consisting of alkali feldspar (albite/orthoclase) and quartz that supposedly coincides with a fault striking N48E and dipping 52SW (I have not personally seen the fault). Most of the vein is covered by colluvium, but in places it can be found on the surface as quartz float. Much of the feldspar is decomposed to the point where it crumbles easily in the hands, even when encountered several feet under the surface of the vein outcrop. The vein opens up into pockets to about 10 cm, and very rarely to 25 cm, in which the quartz crystals (including many Japan Law twins) form along with allanite and small crystals of titanite. The hanging wall of the vein abuts against a clay layer of unknown thickness, and it is along this contact that many of the finest twins are found. Allanite is present in many of the small pockets as jet-black crystals up to 3 cm, but in many cases the crystals are metamict due to the presence of radioactive thorium. Small crystals of reddish-brown titanite up to 6 mm are present in these pockets, usually sprinkled upon the quartz/feldspar matrix and even a few of the quartz crystals themselves.

Smoky quartz crystals from Mina Tiro Estrella can be pale to dark smoky in color, but the vast majority of the crystals found are pale to medium smoky (most likely caused by natural radiation of thorium present in the allanite). Single prismatic crystals usually have not grown much larger than 4 cm (occasionally up to 7 cm) and exhibit the Tessin habit. Japan-law twins are common. Most of the crystals have very pronounced striations running perpendicular to the C axis, and coupled with brilliant luster, make for very dazzling specimens. Occasionally crystals with a dull or matte luster are found, but these can be considered a minority. Surprisingly, the Japan-law twins are usually much larger (up to 10 cm on a side) than the regular Tessin-style crystals. Back in the late 1970's and early 1980's Dick Jones marketed many very dark twins that nobody else has ever found, so some questions exist as to whether or not the color of these is completely natural.
[Philip Simmons 2013]

Structure: Rio Grande Rift Lincoln County Porphyry Belt

Deposit: 3-4 times background radioactivity.

Deposit type: Alkaline complex associated zircon

Ore(s): Fractures Or Shears

Other Databases

Link to USGS MRDS:	10111411

Other Regions, Features and Areas containing this locality

References