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Deposit Type
 
Gold OccurencesGold occurrences in the Pickle Lake mining camp are classic examples of deposits grouped under the descriptive model of Archean low-sulphide Au-quartz veins.  This deposit type is also known as shear-zone-hosted gold, Archean quartz-carbonate vein gold deposits, Archean lode gold and Archean mesothermal gold.  This category of gold deposit is found in every major Archean craton and accounts for worldwide historic gold production in excess of 9,900 tonnes of gold, second only to the Witwatersrand modified paleo-placer gold deposits of South Africa.

The fundamental characteristics of the gold deposits in the Pickle Lake mining camp are summarized as follows:

  • Temporal Range: Archean, Pickle Lake greenstone belt, Pickle Crow assemblage dated at 2705 +/- 2 Ma, Confederation assemblage dated at 2680 +/- 1 Ma.Host

  • Rock Types: The major Au orebodies at Pickle Lake are hosted by the Pickle Crow assemblage which includes mainly tholeiitic lavas, with banded iron formation, and minor calc-alkaline intermediate volcanic/volcaniclastic lithologies as well as quartz-feldspar porphyry intrusive rocks. 

  • Paleotectonic Setting: Most gold deposits in the Superior Province are found in Archean greenstone belts or their associated intrusions along highly deformed steeply dipping major shear zones.  Such shear zones form at major structural discontinuities near the contact between major sedimentary and/or volcanic sequences.  In the Pickle Lake camp there is no major structural dislocation similar to the Destor-Porcupine or Larder Lake-Cadillac Breaks in the southern Abitibi Belt.  However, there is substantial shearing associated with the gold mineralization and the important deposits are near the boundary between two major volcanic sequences, the Pickle Crow and Confederation assemblages.

  • Structure: The gold-bearing veins at Pickle Crow fill pre or syn-ore faults, shears and fractures in the various host rocks.  Auriferous sulphide zones that are stratabound and contained within iron formation occur adjacent to shear zones in some areas.  

  • Associated Deposits: A small amount of scheelite was taken from the Pickle Crow Mine during World War II.  An unrelated deposit types in the Pickle Lake greenstone belt is magmatic Cu-Ni-PGE at the Thierry Mine.

  • Primary Ore Mineralogy: The ore is contained in quartz veins that are generally banded with tiny streaks of tourmaline, chlorite or sericite, and fracture fillings.  Quartz is by far the main vein mineral along with lesser carbonates including siderite, ferruginous dolomite, and calcite.  Minor albite, chlorite and sericite, and local traces of tourmaline and scheelite have been noted.  Native gold is the main ore element at Pickle Crow.  The main sulphide minerals are pyrrhotite and pyrite which combined are usually <2% of the ore material, along with trace arsenopyrite, magnetite, chalcopyrite, galena and sphalerite. 

  • Wall-Rock Alteration: Alteration of wall rocks adjacent to veins and breaks is a prominent characteristic of Archean low-sulphide gold deposits.  At Pickle Crow alteration minerals include silica, sericite, chlorite, carbonate and pyrite.

The Archean low-sulphide gold-quartz vein model is considered to be the main conceptual model that is relevant to the Pickle Crow Property. 

 

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