Gold abundance and an aluminosilicate-rich alteration zone in the Val D'Or mining district, abitibi, Quebec: Examples of the fossil geothermal fields |
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| Authors: | Mehmet F Taner |
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| Abstract: | Investigation of gold abundance in a gold-rich mining district by accurate analytical techniques (e.g., Instrumental Neutron Activation and/or Radiochemical Neutron Activation) shows that gold is anomalously distributed in some parts of the Val d'Or mining district of Quebec. It is possible to distinguish: (1) background values (1.4–3.5 ppb Au); (2) zones of primarily anomalous gold values around the Lamaque-Sigma mines (median: 15 ppb Au); (3) enrichment halos around gold orebodies (median: 70 ppb Au); (4) secondary gold enrichment in shear zones; and (5) high background values for the East Sullivan Monzonitic Stock. The Bourlamaque batholith is considered to be a gold-enriched intrusion because of areas (shear zones) that are anomalously enriched in gold (median: 10 ppb Au). It is concluded that there are auriferous geological units in the Val d'Or mining district, such as the Bourlamaque batholith and Val d'Or Formation. The latter contains the Lamaque-Sigma gold mines, representing 49.6% of the total gold production in the district. It is interpreted that the Val d'Or Formation is part of a central volcanic complex within an island arc system, that the centre of this complex is located in the main Lamaque plug, and that this environment may be compared to high-temperature active geothermal systems which are commonly responsible for the formation of epithermal gold deposits. The Lamaque-Sigma area is considered to be a fossil geothermal field, potentially explaining the anomalous gold values. In addition, a dumortierite-bearing, aluminosilicate-rich zone of hydrothermal alteration in the Val d'Or mining district is considered, as for other similar occurrences, to be the result of hydrothermal alteration within a geothermal field producing an Al- and Si-rich leached protholith which has subsequently been metamorphosed and deformed. A model is proposed for the formation of the gold deposits within the primary gold-rich environment, by mobilisation of gold in the volcanic rocks due to metamorphism and deformation. Therefore, two distinct and successive events are postulated: (1) gold-rich synvolcanic geothermal activity; and (2) late remobilisation from the host rocks, followed by deposition of gold ore within favourable structures. |
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