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LocalitiesCobriza mine ("Corbriza mine"), Chinchado-Sacramento mining district, Pabellón, Tierra Amarilla, Copiapó Province, Atacama, Chile

18th May 2017 19:48 UTCStephen Richard

05589100016048626307533.jpg
I obtained a specimen with one surface covered by calcite with embedded 2-3 mm shiny chalcocite crystals from Minerat (Roberto Rojas Rivera). The substrate is altered feldspar porphyry. Etching the calcite away revealed that the chalcocite crystals are growing on a granular fine-grained adamantine-metallic black mineral that looks more like one of the ruby-silver sulfosalts.

Chalcocite and calcite, pre-etch
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, chalcocite on mystery mineral substrate, after etch
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, chalcocite on mystery mineral substrate, after etch


I asked Mr. Rivera for any other information he might have about the mineralogy from the site (indeed the Cobriza, not the Manto Cobriza), and he provided the following (translated from Spanish):

Chemical analysis of samples from the mine yield copper, iron, nickel, silver, and minor cadmium and selenium.

It is a shallow mine, hosted in andesite with veins of copper and other base-metal sulphide minerals. Some nice azurite crystals have also been found.

18th May 2017 19:56 UTCErik Vercammen Expert

A first generation of fine-grained chalcocite?

19th May 2017 14:43 UTCReiner Mielke Expert

"adamantine-metallic black mineral that looks more like one of the ruby-silver sulfosalts." does it scratch red? If not then like Erik says or you will need to get it tested to be sure, as there are a lot of black metallic mineral species it could be.
 
Mineral and/or Locality  
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