Unusual secondary copper assemblages from deposits in eastern Australia

摘要

Recent open-cut mining operations associated with Cu and Cu-Au orebodies in eastern Australia have revealed a number of exotic assemblages of secondary minerals. The cases examined here all feature secondary phosphates or arsenates and other rather rare species; each of them is noteworthy in terms of the abundance of material that has been recovered. In the Northparkes E22 and E27 deposits at Goonumbla, New South Wales, upper oxidation zones are dominated by libethenite and pseudomalachite, with azurite and malachite emplacement at greater depths. In the nearby E26 deposit, oxidation associated with much more saline (NaCl) ground waters has led to extensive development of sampleite in the phosphate assemblage. Lower in the profile much atacamite was present. A similar pattern of zoning is associated with the oxidized zone of the Girilambone mine, at Girilambone, New South Wales, Secondary copper phosphates were encountered at all levels of the oxidized zone but were particularly pronounced in the upper benches. Deeper in the profile, abundant crystalline native copper was encountered, together with magnificent groups of azurite crystals. Related secondary copper arsenates conspicuous in a paragenetically early sequence of the oxidized zone of the New Cobar mine, Cobar, New South Wales. Associated phases were bayldonite, duftite, gartrellite, agardite, mimetite and various arsenic-bearing members of the jarosite supergroup. A later carbonate sequence (azurite-malachite) was superimposed on this assemblage.