Cartoon to show the different types of placer deposits from the source area to the. Ore deposits placer deposits hydraulic sorting concentration of heavy minerals in regions of low. Though scarce, gold is concentrated by geologic processes to form commercial deposits of two principal types. When heavy, stable minerals are freed from their matrix by weathering processes, they are slowly washed downslope into streams that quickly winnow the lighter matrix. Gold placers and their geologic environment in northwestern park county, colorado by quentin d. Placers can be classified as eluvial, alluvial, eolian, beach, and fossil paleo deposit types. For the love of physics walter lewin may 16, 2011 duration. Pdf ten placer deposit models from five sedimentary environments. Gold is relatively scarce in the earth, but it occurs in many different kinds of rocks and in many different geological environments. The process of erosion concentrates denser minerals, most notably gold, into. Placer materials must be both dense and resistant to weathering processes. Placer mineral deposits a short series of lectures prepared for the fourth year of geology, tanta university 2012 20 by. Placer deposits result from weathering and release of gold from lode deposits, transportation of the gold, and concentration of the gold. Reprintedfrommineralinformationservice,volume17,nos.
Traceelement characteristics of different pyrite types in. Placer deposits were at the center of the great gold rushes of the nineteenth century in california, alaska, the yukon, south africa and elsewhere. Placer deposit, natural concentration of heavy minerals caused by the effect of gravity on moving particles. These are rocks that have been altered by heat and pressure so much so that they become another rock type. A lone prospector with a gold pan can verify the existence of a placer gold deposit in a short period of time. Placer mining, ancient method of using water to excavate, transport, concentrate, and recover heavy minerals from alluvial or placer deposits. The placer can be an accumulation of valuable minerals formed by gravity separation during sedimentary processes.
Geology of placer deposits i mi%i w 2mm in size that are known as nuggets. Lode deposits are contained within surrounding rock whereas placer deposits are dust particles contained in streams and stream beds. Gems and placersa genetic relationship par excellence mdpi. Being at or near the ground surface, placer deposits are easy to mine, do not require the complex and expensive machinery needed for other types of deposits and provide almost immediate rewards to. Animation of a 3d scan of a sample with high gold grades. A slower part of the stream includes the classic placer targets.
Using highresolution imaging techniques, the researchers were able to visualize a to date unknown oreforming. Gold lode and placer mines are located mostly in western states and alaska while production in nevada and california accounts for 70% of domestic production. Placer deposit area in a stream or river where heavy material settles after being carried downstream in the current of the river or stream. Gold, platinum and diamond placer deposits in alluvial.
Man most likely first obtained gold from placer deposits, more than 6,000 years ago. The united states is the second largest gold producing nation in the world. Geological and geographical characteristics of gold mines. Cronan, underwater minerals 1980 hot industrial metal future energy, hightech metals industrial, economic where specific gravity density relative to h 2o 1. Placer gold deposits form via gravity, with the density of gold causing it to sink into trap sites within the river bed, or where water velocity drops, such as.
Streams, gulch and fan placer deposits streams placer deposits in streams are found where. Traceelement characteristics of different pyrite types in mesoarchaean to palaeoproterozoic placer deposits. Three geologic conditions are usually operative in the formation of placers. Monazitebearing placertype deposits can occur in residual weathering zones, beaches, rivers and streams, dunes, and offshore areas. Placers are mineral deposits formed by the mechanical concentration of minerals from weathered debris. Introduction ore deposits are crustal concentrations of useful elements that can be exploited at a pro. Types of placer deposits include alluvium, eluvium, beach. Placer mining is an important source of gold, and was the main technique used in the early years of many gold rushes, including the california gold rush. Examples of deposits mined by means of this technique are the goldbearing sands and gravel that settle out from rapidly moving streams and rivers at points where the current slows down. Placer deposits are sourced from preexisting gold deposits and are secondary deposits. However, some ancient placers, or paleoplacers,are found in sedimentary rocks. Production figures from the wellknown witwatersrand supergroup placers illustrate their productivity relative to other types of gold deposits figure 9.
Placers account for more than twothirds of the total world gold supply, and roughly half of that mined in the states of california, alaska, montana, and idaho. Placer deposits are formed by alluvial processes within rivers and streams, and on beaches. Bauxite forms on granite that has experienced major leaching in tropical areas. Slngewald abstract the placer district of northwest park county covers more than 250 square miles. There are two general types of placer depositsresidual placers and transported or alluvial placers. Mcqueen crc leme, australian national university, canberra, act 0200 and school of rehs, university of canberra, act 2601. Placers may be defined as surficial mineral deposits formed by the. Thus, in the example cited above, placer gold is a mineral deposit type, and all placergold deposits share a set of common geological attributes. Thorium occurrences, geological deposits and resources. Kinds of placer deposits a placer deposit or placer is a deposit that formed in moving water where particlespieces of gold andor other dense minerals have accumulated because the water flow isnt sufficient to keep them moving in many cases, for a placer deposit to accumulate gold over time, the water must be moving fast enough to flush out lighter sand. Mineral sands mineral sands are deposits of ilmenite and other heavy minerals that are concentrated by weathering and beach processes.
Parent rocks regarded as sources have a wide range in composition mainly magmatic and metamorphic and age archean to phanerozoic. Desert placers desert placers in the southwest occur under widely varying conditions but taken as a whole, they are so different from normal stream placers as to deserve a special classification. Alluvial and placer mineral deposits geology for investors. Placer deposits mineral deposits formed by the concentration of moving particles through wind or water action are called placer deposits. Geology of placer deposits by jenkins, olaf pitt, 1889publication date 1970 topics placer deposits publisher san francisco state of california division of mines and geology. Residual placers a residual placer is, in effect, a concentration of gold or other heavy mineral at. This may be done by openpit also called opencast mining or by various surface excavating equipment or tunnelling equipment placer mining is frequently used for precious metal deposits particularly gold and gemstones, both of which are often found in alluvial depositsdeposits of sand and. Small placers are also relatively easy to mine, and the ore. In both, the original source of the gold was in lodes, veinlets, stringers, or stockwerks in solid rock. To accumulate in placers, mineral particles must be significantly denser than quartz whose specific gravity is 2. Classification of mineral deposits geology for investors. Pdf concentration of heavy minerals in placer deposits steps for making a placer mineral deposits placer locates types classification of. Harraz, 20 furthermore, placer deposit is a region known for anthropogenic activities such as. Stream placers, by far the most important, have yielded the most placer gold, cassiterite, platinum, and gemstones.
Pdf traceelement characteristics of different pyrite. Gold deposits are found in different types of rocks and geologic formations, falling into two mining categories. Residual placers it is a type of deposit formed at, or near, the point of release of mineral from the parent rock. Types of placer deposits include alluvium, eluvium, beach placers, and paleoplacers. Hard rock gold resources are reported on the property, but global gold plans to explore for those types of deposits only after the placer deposits are in production.
Pdf placers deposits are now known from five sedimentary environments. The reason so much of it has been mined from placers is that placer deposits are usually easier to locate than lode deposits. Sinceanestimateofthepotentialwealthofthe desertplacersdependsuponfurtherexplorationand miningofthem,itisnotyetpossibletoevaluate. The mineral examiner should learn to recognize flood gold deposits and equally important, he should be fully aware of their pitfalls. The name is from the spanish word placer, meaning alluvial sand. Coastal placer deposits in the china seas mainly exist in sandy and sandygravel coasts and formed primarily during the late pleistocene and holocene liu, 1989. Sketch illustra ting formation of placer gold deposits. Mineral sands mineral sands are deposits of ilmenite and other heavy. Most of the placer deposits being mined today are cenezoic or younger and occur in unconsolidated materials. Special report 89 gold, platinum and diamond placer deposits in alluvial gravels, whitecourt, alberta g. Placer deposits include several different types of commodities and a range of geological environments. Placer deposit and different forms of deposition adapted from placer mine deposits p. There are various types of placer deposits, classified based on their formation.
1320 109 404 1133 803 74 368 1274 412 1318 1442 1436 731 262 507 1543 753 544 1156 1225 1147 1467 1344 1386 802 1170 241 1498 103 1151 1156 1466 288 865 1328 689