Reconnaissance for Mississippi Valley-type Zn-Pb deposits in the Franklinian Basin, Eastern North Greenland. Results of the 2012 Season

Two new Zn showings were discovered within the same general stratigraphic horizon, one in Western Melville Land (Peary Land) and the other in Kronprins Christian Land, Eastern North Greenland, during exploration reconnaissance carried out by the Geological Survey of Denmark and Greenland (GEUS) in the summer of 2012.

Mineralisation consists of lime-green sphalerite and minute traces of galena and sulfosalts, in calcite, dolomite, and, occasionally, fluorite veinlets and pockets. These veinlets and pockets are intermittently distributed within dolostones of the upper part of the Turesø Formation (Upper Ordovician to Lower Silurian – Morris Bugt Group), of the Franklinian Basin carbonate platform. Recorded zinc grades, for these Mississippi Valley-Type (MVT) showings, are variable due to the irregular distribution of relatively coarse-grained sphalerite. The highest grade recorded is 5.81% Zn, with most mineralised samples having Ag and Pb concentrations below the detection limit.

It is suggested that metal precipitation, from basinal brines circulating within the upper part of the Turesø Formation, was promoted by reduced sulphur derived from the reduction of evaporite sulphate likely initially present in immediately underlying beds. These underlying beds were likely to have contained evaporites, since desiccation cracks, documenting their subaerial exposure were identified. The reduction of sulphate to sulphide could have been caused by the reaction with organic matter since the pale yellow colour of these underlying beds suggests the organic matter, presumably present originally, has been consumed in that process.

Furthermore, two float samples collected in Samuelsen Høj Formation carbonate mounds in Melville Land (Peary Land) were found to be mineralised or anomalous in zinc. The mineralised float contains fluorite and weathered sphalerite and yielded 3.58% Zn and 263 ppm Pb. The anomalous float yielded 140 ppm Zn. This suggests that some mineralising fluids moved up the stratigraphy and could have been collected in this formation, underneath the Lauge Koch Land Formation turbidites, which would have acted as an important aquitard.