Gold and base metal potential of the Ingia area, central West Greenland

The Íngia area in the northern Umanak district consists mainly of Archaean gneiss and Lower Proterozoic supracrustals, the Karrat Group. The latter was deposited in an epicontinental back-arc basin and comprises a thick basal unit of shallow marine quartzites overlain by a thin wedge of mafic metavolcanics followed by a thick sequence of metaturbidites. The rocks were folded and metamorphosed during the 1.8 Ga Rinkian orogenesis.

Stratiform mineralisation of exhalitic or sedimentary origin occurs at several levels in the supracrustal pile. It is typically developed as laterally consistent cherty pyrrhotite-graphite breccia with base/noble metal contents in the order of 2700 ppm Zn, 500 ppm Cu and 40 ppb Au. Additionally, disseminated arsenopyrite mineralisation with 100-1000 ppm As and 4-7 ppb Au is known from local boulders. The stratiform mineralisation offers in itself possibilities for economic metal concentrations, and also provides potential source rocks for epigenetic mineralisation.

Epigenetic quartz vein mineralisation is mainly known from boulder finds. It is dominated by pyrrhotite, but also chalcopyrite and occassional galena, sphalerite, scheelite, molybdenite and arsenopyrite occur. Metal contents of up to 1.4 ppm Au, 2.17. As, 1.3% Zn and 0.9% Cu have been encountered. An outcropping mineralisation of chalcopyrite-bearing quartz veins is probably controlled by a low-angle thrust zone, a characteristic structural element in the region.

A geochemical survey using stream sediment samples and pan samples has outlined three areas anomalous in gold and a number of ether elements. The highest gold values are 33 ppb in stream sediment samples and 19 ppm in pan samples. The gold is probably hosted in arsenopyrite and ether sulphides.

The Íngia area holds a potential for gold-bearing quartz veins. Outcropping mineralisation of this type can be expected in the anomalous areas pin-pointed by geochemistry. A potential for stratiform copper-zinc deposits also exists, but this type of mineralisation should be explored for on a regional scale. In general, the study indicates that the metaturbidites of the Karrat Group are highly arsenical and constitute a promising regional target for gold exploration.