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Placer scheelite and gold from alluvial sediments as indicators of the primary mineralization – examples from SW Poland

Mikulski S.Z., Wierchowiec J.

Geological Quarterly

2013

Vol. 57, No. 3

503–-514

Detailed morphologic studies of detrital scheelite and gold grains from clastic Cenozoic sediments (alluvial and eluvial-colluvial) in two selected areas of the Lower Silesia region allowed to describe their specific features (size, roundness, lustre, and lack or remnants of primary intergrowths with other minerals). It allows estimating length of hydrodynamic transport and distance from the source area. Such features are also an important tool in determining the source of ore mineralization and to establish the parent area for detrital accumulations. Moreover, electron microprobe (EMPA) investigation of detrital gold allowed to recognized internal structure and chemical composition of placer gold grains. The grains commonly revealed zonal structures due to chemical supergene gold mobility recognized nearly in all studied pan-concentrate samples.

Orogeniczne żyłowe złoża złota i ich rozsypiska a największe światowe gorączki złota w drugiej połowie XIX wieku w Ameryce i Australii

Mikulski S. Z.

Przegląd Geologiczny

2009

Vol. 57, nr 12

1048-1056

The paper presents geological, ore-mineralogical and economic characteristics of the goldfields in the Western USA (California and Yukon) and Australia (Bendigo-Ballart and Kalgoorlie regions). Moreover, common geological features of these areas, which were the place of modern Gold Rushes from the second half of 19th c. to the beginning of 20th c. are also described. Thanks to discovery of gold, these inhabited areas became the land of promise for millions of people and gold production contributed to economy of the fast growing nations. The first period of Gold Rushes began in California (USA) and Bendigo-Ballart region in Victoria (Australia) in 1848 and 1851, respectively. Placer gold was discovered first in Cenozoic alluvial sediments and subsequently in auriferous quartz lodes, which were the source of detrital gold. The detrital sediments appeared extremely rich in gold nuggets. The biggest nuggets, ca. 65.2 and 24.5 kg in weight, have been found in Bendigo and California, respectively. Placer gold production during the Gold Rush in California from 1848 to 1864 is estimated at ca. 1300 Mg Au. Since 1850, prospectors begun to discover numerous gold-bearing quartz veins (Mother Lode system) along the Sierra Nevada in California. These auriferous lodes gave over 1100 Mg of gold. In Bendigo-Ballart goldfields about 480 Mg of gold was extracted from placers and 260 Mg goldfrom from auriferous quartz veins in the years 1851–1861. The second period of modern Gold Rushes took place again in America (Yukon) in 1896 and in the Western Australia (Kalgoorlie) in 1893. In Yukon, gold was mainly extracted from Cenozoic river’s gravels (> 311 Mg) and in Kargoorlie—mainly from auriferous quartz-carbonate lodes. Some of goldfields with auriferous lodes discovered in 19th c. are still in production. Best example is here the Kargoorlie deposit that became recently the 3rd largest world producer of gold (> 1600 Mg Au). Gold production from lodes in California, Bendigo-Ballart and Kalgoorlie is roughly estimated at > 4000 Mg. Gold-bearing lodes formed as results of migration of fluids of various origin and gold precipitation in the upper crust within post-collisional tectonic settings. These lodes belong to orogenic type of gold deposits hosted by greenstone schist belts in metamorphic terranes of various age. Primary gold is bound mostly by auriferous sulphides—arsenopyrite and pyrite and as native gold which infills fractures in quartz and breccias. In California, Yukon and Victoria, rich placers were formed in the Cenozoic during exhumation of metamorphic terranes hosting auriferous gold lodes.