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TitleInterpretation of borehole gravity data of the lalor volcanogenic massive sulfide deposit, Snow Lake, Manitoba, Canada
AuthorSchetselaar, E; Shamsipour, P
SourceInterpretation vol. 3, no. 3, 2015 p. T145-T154,
Alt SeriesEarth Sciences Sector, Contribution Series 20150092
PublisherSociety of Exploration Geophysicists
Mediapaper; on-line; digital
File formatpdf; html
AreaSnow Lake
Lat/Long WENS-102.0000 -100.0000 55.0000 54.7500
Subjectsgeophysics; economic geology; mineral exploration; mapping techniques; boreholes; gravimeters; geophysical logging; rhyolites; mineral deposits; volcanogenic deposits; gravity anomalies; bouguer gravity; bouguer anomalies; lithofacies; lithology; igneous rocks; volcanic rocks; intrusive rocks; rhyodacites; metamorphic rocks; gneisses; schists; structural features; faults, thrust; displacement; metamorphism; hydrothermal alteration; lithogeochemistry; mineralization; Lalor deposit; Flin Flon greenstone belt; Trans-Hudson Orogen; volcanic-hosted massive sulphide deposits; data processing; Precambrian
Illustrationsgeological sketch maps; profiles; tables; scatter diagrams; sections; plots
ProgramTargeted Geoscience Initiative (TGI-4), Methodological Development
AbstractWe have acquired borehole gravity data along five drillholes intersecting the Lalor volcanogenic massive sulfide deposit hosted in the eastern Flin Flon greenstone belt at Snow Lake, Manitoba, Canada. Inverted apparent interval density (IAID) logs were calculated from the borehole gravity data and compared with lithofacies and Zr/TiO2 logs; the latter of which is a geochemical proxy for differentiating volcanic rocks of felsic to mafic composition. The IAID anomalies predominantly reflect alternating mafic and felsic volcanic rock units in the footwall and hanging wall of the massive sulfide deposit. IAID lows are associated with Zr/TiO2 highs that correspond to rhyolite and rhyodacite intervals in the hanging wall. IAID lows with associated Zr/TiO2 peaks in the footwall occur within intervals of gneiss and schist formed by metamorphism of hydrothermally altered rocks, suggesting that these IAID lows still reflect the felsic composition of their volcanic protoliths. A significant peak-to-peak Bouguer anomaly of 0.66 mGal caused by an estimated excess mass of 0.7 mT can be correlated with gamma-gamma density signature of the main sulfide ore zone in three boreholes. This anomaly is aligned with the ore zone after restoring the displacement along a northeast-dipping structure. When integrated with drillhole lithology and lithogeochemistry logs, gravity borehole data can, in addition to the direct detection of mineralization, be used as a subsurface geological mapping tool.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. Borehole gravity data have been collected in February 2014 in five drill holes in the Lalor mine camp, Snow Lake, Manitoba. Since 2008 borehole gravity sensors have been developed that are small enough to be lowered in drill holes to provide information on the density distribution of geological formations at depth including metallic ore deposits. The gravity data have been interpreted by comparing the calculated density variations along the boreholes with geochemical and geological information. In one of the five drill holes a significant gravity anomaly was found that is caused by a dense mass close to the drill hole. This extra mass is possibly explained by undiscovered sulphide mineralization, because it occurs in the same rock units at comparable depths to the known mineralization elsewhere.