Ore Types And Fluid Regimes: Macassa Gold Mine, Kirkland Lake
The Macassa Mine is the only remaining gold producer of seven inter-connected mines which comprise the Kirkland Lake mining district. The district has produced more than 710,000 kg Au since 1913 from quartz veins and lodes within the Archean Timiskaming Group.;There are 3 types of gold ore at the Macassa Mine: (1) native Au in chloritic fault gouge or small quartz lenses within a prominent, subvertical, thrust-fault system. This is called Break ore. (2) gold-bearing quartz veins in both hanging and footwalls of this fault system. This is called Vein ore. (3) several zones in the deep west part of the mine which are very fractured, bleached, silicified and pyritized rock containing lenses and pods of quartz with native Au and telluride minerals. This is called Breccia ore.;Calculations of chemical mass balance indicate the principal chemical transfers in hydrothermal alteration of wall rocks adjacent to ore involved additions of CO(,2), but minor additions or subtractions of Fe(,2)O(,3), MnO, MgO and CaO, which alters Fe, Mg, Ca, Mn-silicate minerals in wall rocks to Fe, Mg, Ca, Mn-carbonate minerals. Additions of K(,2)O along with depletions of Na(,2)O reflect the hydrolysis of albite to muscovite, and minor gains of SiO(,2) plus S are evident in the coprecipitation of quartz and pyrite.;Geostatistical analysis of gold distribution within a type zone of Breccia ore at Macassa indicates a general continuity which can be approximated by theoretical semivariogram models. However, experimental semivariograms calculated along three principal directions within the type zone: alone strike, across strike, and down dip; have zonal, directional and proportional effect anisotropies.;The (delta)('18)O and (delta)D of rocks and mineral separates in these 3 ore types suggest the ore was precipitated from hydrothermal fluids of (delta)('18)O +7 to +9.6 per mil, (delta)D -35 to -85 per mil, and at 380 to 490(DEGREES)C. These data are consistent with fluids evolved by dehydration of volcanic and sedimentary rocks, which ascended by seismic pumping along pre-existing faults and fractures and deposited gold within faulted and fractured syenites and Timiskaming Group rock.;Isotopic abundances and the oxidation state of iron in rocks within portions of the major faults and non-auriferous veins suggest subsequent incursions of oxidizing fluids of marine and meteoric origin.
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