Abstract

In the central East Greenland Caledonides there are numerous occurrences of strata-bound copper mineralization and hydrothermal arsenic and tungsten mineralization. The host rocks are metasediments of middle Proterozoic and unmetamorphosed to slightly metamorphosed late Proterozoic sediments (quartzite, shale, limestone), all intruded by Caledonian granites.Strata-bound copper mineralization 0.2 to 2 m thick is found at different stratigraphic levels in late Proterozoic shale and quartzite and extends over a distance of 275 km. The mineral assemblages in the shale are dominated by chalcopyrite-pyrite, bornite-chalcocite, or chalcocite. The sulfide associations in the quartzite are chalcopyrite-pyrite-(pyrrhotite) or chalcopyrite-pyrite-(tetrahedrite). In addition strata-bound sulfide-bearing veins occur. The grade of the mineralized zones varies from 0.05 to 1.35 percent Cu. The strata-bound copper sulfides were probably concentrated mainly by diagenetic processes but later were modified by metamorphic mobilization and locally enriched by hydrothermal solutions.Hydrothermal scheelite and arsenopyrite mineralization is located mainly close to the border zone between the Central Metamorphic Complex and the late Proterozoic sediments.Three main types of scheelite mineralization occur: (1) a skarn type, (2) a vein type, and (3) a breccia type. The skarn type is hosted by marble, schist, and calc-silicate rocks. The tungsten content varies from 0.1 to 1 percent W with enrichment of the elements Be, Bi, F, Li, and Sn. Scheelite mineralization in quartz veins yields 0.1 percent W associated with enhanced contents of As, Be, Bi, F, Li, Pb, and Sn. The skarn and vein types are closely related to Caledonian granitic intrusions. The scheelite (+ or -stibnite) mineralized breccia type is found in fault zones probably connected with a granite. These occurrences contain 0.8 to 3 percent W and up to 2.4 Sb and represent at the moment the only mineral deposit of potential economic interest in the area.The arsenopyrite mineralization is regionally widespread. Mineralized quartz veins occur in both quartzitic and semipelitic sediments, whereas mineralized fracture zones are restricted to semipelitic quartzite. The arsenopyrite mineralization is often associated with scheelite, galena, pyrrhotite, chalcopyrite, sphalerite, and traces of gold and silver.The distribution of the elements in the scheelite and arsenopyrite mineralization indicates a zonation around the Caledonian granites. In general, elements such as Be, Bi, F, Li, and Sn are concentrated within 1 to 2 km from the contact. At a greater distance, up to 7 km, the metals Bi, Co, Cu, Pb, and Zn are typical. In terms of fluid inclusions in the veins, the homogenization temperatures of boiling CO 2 -bearing water of moderate salinity are from 225 degrees to 260 degrees C with a pressure of approximately 1 kb.

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