A Passion For Gold: An Autobiography

Glossary

Glossary Note: Definitions reprinted from the 1997 American Geological Institute Glossary of Geology are indicated with (agi, 1997); those that have been modi- fied are noted. Allochthon. A mass of rock or fault block that has been moved from its place of origin by tectonic processes, as in a thrust sheet or nappe (agi, 1997). Alluvium (alluvial). A general term for clay, silt, sand, gravel, or similar unconsolidated detrital material, deposited during recent geologic time by a stream or other body of running water (agi, 1997). Anticline. A fold, generally convex upward, whose core contains the stratigraphically older rocks (agi, 1997). Antler Orogeny. A late Paleozoic orogeny, named after Antler Peak at Battle Mountain, Nevada (Roberts, 1949). Lower Paleozoic rocks deformed during this orogeny here are unconformably overlain by Lower Pennsylvanian strata. However, in Eureka County, Nevada, Roberts (1951) and Roberts and others (1965) recognized that the orogeny spanned from late Devonian to Middle Pennsylvanian time. The orogeny consists of two major phases (Roberts and Madrid, 1990): (1) episodic early thrusting, ending in late Mississippian time, of Lower to Middle Paleozoic oceanic chert, shale, quartzite, and volcanic rocks onto coeval shallow-water carbonate rocks of the continental margin on the Roberts Mountains thrust, and (2) subsequent uplift along the Antler Orogenic Belt during latest Mississippian and Pennsylvanian time, causing clastic rocks to be shed into eastern Nevada and western Utah. The orogenic belt extends southward into southern Nevada and northward into the Mackay area, Idaho (Skipp and others, 1979), and into the Colville area, Washington (Bennett, 1937). Antler Sequence. A sequence of Pennsylvanian and Permian beds that were deposited on rocks deformed during the Antler Orogeny. In the Antler Peak area they consist of the Battle Formation, Antler Peak Limestone, and Edna Mountain Formation. Autochthon. A body of rock in the footwall of a fault that has not moved substantially from its site of origin (agi, 1997). Glossary 211 Breccia. Broken rock composed of angular fragments as in a fault zone. Also used for sedimentary units composed of angular fragments. Carbonate shelf. A broad shallow-water platform on which carbonate rocks were deposited, bounded by a shelf margin and a relatively steep slope into deep water. Carlin-type gold deposit. A type of low-temperature (150–270 degrees Centigrade ) gold deposit characterized by arsenic, antimony, mercury, and thallium as trace elements. The fine-grained gold is in the range of one to thirty microns. It cannot be recovered in a pan but can be analyzed chemically and by fire assay. Carlin-type gold deposits were first recognized near Carlin (Lynn district), Nevada, and defined by Roberts, Ketner, and Radtke (1967). They have also been called “deposits of invisible gold.” Chalcopyrite. Copper, iron sulfide. Weathers to secondary copper minerals, malachite (green), and azurite (blue). Chert. Rock composed of hard, fine-grained (cryptocrystalline) silica. Chlorite. An iron, magnesium, hydrated silicate, generally dark green to black. Chrysocolla. Copper silicate (green). Craton. A part of the Earth’s crust that has attained stability and has been little deformed for a long period of time. Areas are largely Precambrian in age (agi, 1997). Detritus. Sedimentary debris or alluvium carried out into a valley or trough. Dike. A tabular igneous intrusion that cuts across the bedding or foliation of the country rock (agi, 1997). Eluvial. Debris derived from rock weathering in place, which has undergone little transport. Eugeosyncline. A geosyncline in which volcanism is associated with clastic sedimentation; a volcanic part of an orthogeosyncline, located away from the craton (Stille, 1940) (agi, 1997). Fanglomerate. A sedimentary rock consisting of waterworn fragments of various sizes deposited in an alluvial fan (agi, 1997). Fault. A break in the earth’s crust along which one side may move relative to the other side; commonly steep. Feldspar. Potassium, sodium, or calcium aluminum silicate, weathers to clay. Fracture. A break in the earth’s crust along which there is little or no movement ; may be zones of weakness along which magma and mineralizing solutions might rise. Galena. Lead sulfide, weathers to white lead carbonate or sulfate. Golconda thrust fault. A major thrust fault commonly associated with the Sonoma Orogeny of late Permian and/or earliest Triassic age, which carried oceanic chert, shale, and volcanic rocks east onto shelf rocks of the Antler Sequence and related rocks (Ferguson, Roberts, and Muller, 1952; Silberling and Roberts, 1962). 212 Glossary Hydrothermal deposit. A mineral deposit formed by precipitation...