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Cruzeiro mine, São José da Safira, Doce valley, Minas Gerais, Brazil

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Name(s) in local language(s): Lavra do Cruzeiro (Mina do Cruzeiro)
 
A gemstone and specimen mine in pegmatites.
Safira pegmatite district, Eastern Brazilian pegmatite province.

Note on the mineral list: for "coeruleolactite" see references and information given for Planerite-Turquoise Series.

Mine Information: This is one of the worlds most important gem and specimen mines. It was mined from about 1915, firstly for mica (muscovite), and was a major producer during WWII, after which mining efforts dropped dramatically. In the 1950s, mining resumed for tourmaline and other minerals.

Specimen mine accessed via a 4ft x 5ft adit that intercepts and follows the pegmatites via drifts, winzes, and at least one shaft for ventilation.
Development work utilizes drill+blast, but gem areas are excavated using hand-mining methods.

Regional Geology: In the southeast corner of the Macacos quadrangle a relatively large and arcuate mass of medium- to coarse-grained metagabbro is associated with talc schist and serpentinite in terrain of Rio das Velhas series rocks. The metagabbro consists of actinolite, hornblende, plagioclase (mostly albite), clinozoisite, and zoisite. Commonly the metagabbro is separated from the serpentinite by a zone of talc schist. Evidence found underground at the southwest end of the main level in the Cruzeiro asbestos mine indicates that the metagabbro has been partly altered, or replaced by talc near the contact with the serpentinite. In most places this zone is sheared, resulting in talc schist, although the rock locally retains a gabbroic texture and appearance even when it is composed mostly of talc.

Mine Geology: There are at least five distinct pegmatites worked in the mine. They are hosted by Precambrian quartzites, mica schists and amphibolites. The "amphibolites" are probably altered ultramafics, with olivine, pyroxene and garnet (pyrope). Association minerals indicate the pegmatites are rich in lithium, boron, beryllium, manganese, tin, niobium, tantalum, phosphorus, uranium, and copper.

The pegmatites are classically zoned granite pegmatites and from the border to core the zones are typically:
1. A thin mica rich selvage
2. The main border zone of granitic rock
3. The outer intermediate zone with muscovite rich granite
4. The inner intermediate zone, mostly K-feldspar
5. The central zone, of most I interest mineralogically, with coarse grained quartz and K-feldspar, and vugs with albite, tourmaline and spodumene
6. A quartz core

Since the formation is weathered; with feldspars altered to kaolin, and spodumenes altered to montmorillonite; the tourmalines are typically recovered without matrix. Tourmaline indicators are clevelandite, lepidolite, and coatings of iron-manganese oxides and phosphates.

Mineral List

Mineral list contains entries from the region specified including sub-localities


36 entries listed. 18 valid minerals. 1 (TL) - type locality of valid minerals. 1 erroneous literature entry.

Localities in this Region

Brazil

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References

Rocks & Min.: 63:49 & 53.

Cassedanne, J.P & J.O. (1980): Famous mineral localities: The Cruzeiro mine, past and present. Mineralogical Record 11: 363-367 + 370.

"Gem Pegmatites Of Minas Gerais, Brazil: The Tourmalines Of The Governador Valadares District" by Keith Proctor, Gems & Gemology, Spring, 1985, pp 96-104.

USGS (2005), Mineral Resources Data System (MRDS): U.S. Geological Survey, Reston, Virginia, loc. file ID #10066479 & 10066283 (Cruzeiro #1) & 10105385 (Cruzeiro #2).

U.S. Bureau of Mines, Minerals Availability System (MAS) file ID TC42691 & TC42416 (Cruzeiro #1) & TC42431(Cruzeiro #2).

Bosi, F., Andreozzi, G.B., Skogby, H., Lussier, A.J., Abdu, Y.A., Hawthorne, F.C. (2013): Fluor-elbaite, Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3F, a new mineral species of the tourmaline supergroup. American Mineralogist, 98, 297–303.

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