Metallogeny of the "East South C" ore zone in the Dickenson Mine, Red Lake, Ontario; evidence for syngenetic gold deposition

Abstract

<p>The Dickenson Mine, a gold producer in the Uchi volcanic-plutonic subprovince of the Canadian Shield, lies along the eastern flank of a volcanic complex consisting mainly of massive to pillowed basaltic komatiites and magnesium tholeiites with some ultrabasic and felsic flows, chemical and clastic sediments and proximal volcaniclastites. Studies of the 17, 22, 24, 25 and 30 Levels in the "East South C" and "East South C Footwall" ore zones show that the gold-bearing horizons lie within stratigraphically conformable fragmental rocks, which have been derived from a source dominated by basaltic komatiites and felsic volcanics with minor cherts and Fe-rich tholeiites.</p> <p>At least two different types of mineralization are recognized. In the "East South C Footwall" zone (25 Level), the mineralization occurs in the metamorphosed argillaceous sediments. Increasing gold content correlates with a strong enrichment in total Fe, MnO, S, As, Zn and Ce, and with moderate increases in MgO, CO2, Ni, Co, Cu, Cr and V. There is also a strong depletion in SiO2, CaO and Ba in the auriferous rocks. The dominant opaques are pyrrhotite and magnetite with accessory pyrite, arsenopyrite and ilmenite. The "East South C" ore zone on the 30 Level is a felsic volcaniclastic horizon enclosed by pillowed mafic volcanics. With increasing gold content samples from this ore zone show a strong enrichment in total Fe, As, S, Zn and Ce and moderate increases in Cr, Ni, V and Ba. There is also a strong depletion in MgO and Zr. Profiles of Au, As and S about this ore zone indicate a strong asymmetry, in that background gold content is greater by a factor of 5 to 20 in the footwall rocks. The dominant opaques are pyrite, pyrrhotite and arsenopyrite with accessory magnetite.</p> <p>These ore zones are pre-tectonic and post dated by at least two periods of lower amphibolite grade metamorphism. The dominant structural element is a northwesterly foliation. In areas of high strain, stratigraphy and mineralization parallel this trend. In areas of low strain, stratigraphy and mineralization trend in a northeasterly fashion and exhibit numerous northwest trending axial planes. The dominant metamorphic minerals are almandine, andalusite, cordierite and amphibole.</p> <p>The metal-rich mineralized zone on the 25 Level is an auriferous sediment in which both chemical (exhalative) and clastic components are recognizable. Low temperature solutions carried and precipitated Au, As, S, Fe, Ti, Mn, Cu, Co, Zn and perhaps Si. MgO, Ni and Cr may have been enriched through leaching or erosion of nearby komatiites. The aluminum and silica content of these rocks indicates a significant detrital component. In the mineralized felsic volcaniclastites on the 30 Level, the precipitation of metals (Au, As, S, Fe, Zn) was synchronous with felsic volcanism or erosion of a felsic source.</p> <p>In conclusion, the "East South C" and "East South C Footwall" ore zones are syngenetic deposits.</p>