Geology of the Kjøkkenbukta orebody, Bleikvassli Gruber, Nordland, Norway

Abstract

The aim of the present study was to obtain more data regarding geological relations between the massive sulfide ore and wall rock, especially the microcline gneiss, the genesis of which is a subject of discussion. Another objective was to get more data about the distribution of gold in the ore and wall rocks. The choice of mapping target was influenced both by geological relationships and interests of the mining company. Mapping of the mining level 290 meters above sea level (m.a.s.l.) was completed during two weeks in April and May, 1996. Both walls and roof along 190 m of the underground workings were mapped in the scale 1:100. The working face of the drifts and some interesting localities on the walls were mapped in approximately the scale 1:50. The contact between the NNW part of the ore zone in the Kjøkkenbukta ore- body and the microcline gneiss body is discordant and the microcline gneiss is wrapped around the ore zone. The relationship between the microcline gneiss and the surrounding mica schist is complicated by superimposed tectonic events. A single observation of an angular unconformity between the schist and micro- cline gneiss can be interpreted in two ways; either as a primary intrusive, or a tectonic contact. Massive ore and wall rocks in the NNW ore zone have discor- dant relationships to each other, and the ore cuts through schistosity and the hinge zones of small F, folds. This is probably a result of tectonic emplacement of the ore along a shear zone. Microscopic recognizable native gold or electrum have not been found in the massive ore of the Kjøkkenbukta orebody. This is an agreement with previously obtained data for the Bleikvassli deposit in general (Moralev et al., 1995) Native gold and electrum have been found in veinlets of remobilized ore and deposition of gold and electrum can be correla- ted temporally with carbonate-chlorite veinlets.