Geologic description
This prospect is one of a group of similar deposits (PA021 to PA031) that are scattered along the south shore of Saginaw Bay, on the peninsula north of Saginaw Bay, and on the Keku Islands. They occur in a heterogeneous section of unmetamorphosed volcanic, carbonate, and clastic rocks that vary in age from Silurian to Triassic (Muffler, 1967). The mineralization generally consists of veins, veinlets, and irregular pods that contain base metals and barite (Still and others, 2002). There are no plutonic rocks in the immediate vicinity; however, the sedimentary rocks are cut by scattered gabbro dikes. The origin of the deposits is uncertain although most appear to be epigenetic. Various origins have been proposed including that they are remobilized massive-sulfide deposits, that they are related to a buried intrusive, or that they are Mississippi-Valley-type deposits. This prospect was first staked in 1923 and was restaked periodically until at least 1931 (Buddington, 1925; Still and others, 2002). The mineralization consists of barite veins, veinlets, and pods that cut a sequence that consists mainly of felsic and mafic volcanic rocks of the Keku Volcanics of Triassic age (Muffler, 1967). Some similar veins and veinlets contain witherite. The veins vary from 0.1 to 2.3 feet thick, extend for up to 200 feet along strike, and occur across a zone about 300 feet wide (Still and others, 2002). The veins generally strike northwest and dip steeply to vertically. The rocks in the immediate vicinity of the mineralization consist of a sequence of felsic volcanics, volcanic breccia, limestone, and conglomerate. The volcanics and conglomerate also contain disseminated pyrite and sphalerite. A sample across a vein about 2 feet thick contained 28.3 percent barite. A sample of conglomerate with disseminated sphalerite and pyrite contained 8,382 parts per million (ppm) zinc. A sample of Carboniferous limestone nearby with disseminated pyrite, sphalerite, and galena contained 5.72 percent zinc and 600 ppm lead. |
