Geologic description
The country rocks at the Avnet manganese prospect include Paleozoic limestone, slate, chert, and greenstone that grade into calcareous schist, quartz-mica schist, and quartzite (Thomas, 1965). The prospect is at or near a northeast-trending thrust fault in the chert unit (Reifenstuhl and others, 1997 [RI 97-15a]).
This poorly exposed deposit reportedly was discovered in 1952 by Paul Bittner (Thomas, 1965). Frost-heaved rock chips at the surface presumably represent rock directly beneath. The rubble reportedly is light colored, weakly calcareous quartzite, schist, and phyllite. Development work consists of a trench 40 feet long, 3-feet wide, and 2 feet deep, two caved pits, and some surface scrapings (Thomas, 1965).
The ore mineral at the Avnet prospect is psilomelane (manganese oxide), which occurs as small, frost-heaved fragments in a zone 3,000 feet long and 600 feet wide at the crest and on the northwest side of a ridge. The psilomelane is in the quartzite, where it forms small, irregular masses up to 3 inches in largest dimension, and in vein quartz, where it forms lattices of thin seams. It also coats some of the rubble. Thomas (1965) speculated that the psilomelane is hydrothermal in origin. Minor pyrolusite occurs with the psilomelane (Foley, 1992). Thomas (1965) collected 32 samples of frost-heaved material in 1964. They assayed 0.64 to 34.4 percent manganese, with an an average value of 15.78 percent. Silver values ranged from below the limit of detection to 0.28 ounce per ton. The samples were assayed for gold but all were below the detection limit. Liss and others (1997) collected a sample (96KC096) of manganese-rich quartz veins in tan, sugary quartzite rubble near a prospect pit. It contained more than 20,000 parts per million (ppm) manganese, and 499 ppm gallium, 195 ppm copper, 220 ppm zinc, and 10.2 ppm cadmium Values of other elements were not anomalous. |
