Tennantite


Composition: Cu6[Cu4(Fe,Zn)2](As,Sb)4S13
Crystal System : Cubic
Colours: Steel-grey, iron-grey, black
Lustre : Metallic
Hardness (H) : 4
Specific Gravity (S.G) : 4.6-4.7
References: Pohwat (2009)

Distribution

Abundant. One of the principle ore minerals widely distributed throughout the deposit. Well crystallised examples occur in all three oxidation zones.

Occurrence

  • Hypogene
  • Supergene
  • 1st Oxidation Zone
  • 2nd Oxidation Zone
  • 3rd Oxidation Zone

Notable Finds

The famous Klein/Kegel collection tennantite in the Smithsonian (# NMNH R8534) with crystals to 185 mm was collected from 6 Level in the first oxidation zone. Most tennantite specimens have somewhat dull, corroded faces, but lustrous metallic crystals to 15 mm were found in the first oxidation zone - again, on 6 Level (Von Bezing, 2007). In the third oxidation zone, on 45 Level, crystals to 30 mm with a good metallic lustre and associated with quartz were recovered.

Paragenetic and General Notes

Tennantite is an abundant component of the hypogene (sulphide) assemblage at Tsumeb. It is therefore a common matrix mineral for many secondary species; indeed, oxidising tennantite is a major source of arsenate ions and some of the base metal cations that come together to form secondary arsenates.

Tennantite is the most important primary copper ore at depth. It occurs as very fine grains in massive sulphide ores, but also as larger solid masses.

Keller (1977) considers tennantite crystals of tetrahedral habit to have formed from the disintegration of surrounding ore matrix, rather than through crystallisation in open spaces.

A small proportion of the tennantite at Tsumeb may be of supergene origin.  This would include, of course, the reported pseudomorphs of tennatite after azurite (Gebhard, 1999).

Tennantite is reported to form pseudomorphs after the following minerals:  azurite (common); enargite (common).

The following minerals are reported to form pseudomorphs after tennantite:  arsentsumebite (rare); austinite (rare); bayldonite (rare); chalcocite (rare); dolomite (common); duftite (rare); enargite (rare); ferrilotharmeyerite (rare); jarosite (rare); malachite (rare); mottramite (rare); serpierite (rare).