Origin of placer gold and other heavy minerals from fluvial Cenozoic sediments in close proximity to Rote Fäule-related Au mineralisation in the North Sudetic Trough, SW Poland

Abstract

1 Uni ver sity of War saw, Fac ulty of Ge ol ogy, ¯wirki i Wigury 93, 02-089 Warszawa, Po land Wierchowiec, J., Zieliñski, K., 2017. Or i gin of placer gold and other heavy min er als from flu vial Ce no zoic sed i ments in close prox im ity to Rote Fäule-re lated Au min er ali sa tion in the North Sudetic Trough, SW Po land. Geo log i cal Quar terly, 61 (1): 62-80, doi: 10.7306/gq.1315 De tailed mor pho log i cal and geo chem i cal stud ies of placer gold grains and other heavy min er als from Ce no zoic flu vial clastic sed i ments in the area of the Zimnik Creek drain age ba sin (North Sudetic Trough, Lower Silesia) al lowed the de scrip tion of their spe cific fea tures: shape and mor phol ogy, flat ness in dex, in ter nal tex tural fea tures and chem i cal com po si tion of the gold grains. It en ables an es ti ma tion of the dis tance from the source area and de ter mi na tion of the source of the ore min er ali sation, along with es tab lish ing the feeder ar eas for placer min er ali sa tion in clud ing Rote Fäule-re lated gold hosted by Rotliegend-Zechstein tran si tional sed i ments. The com par i son of the heavy min eral con tents of placer grains from the Zimnik Creek drain age ba sin makes it pos si ble to iden tify the area of or i gin for the gold par ti cles. The crys tal line Au-Ag-Pd-Hg (polymetallic) al loy grains of flu vial gold are as sumed to come from the tran si tional sed i ments be tween the Rotliegend and the Zechstein in the North Sudetic Ba sin. The mor pho log i cal and geo chem i cal fea tures of the polymetallic grains strongly sug gest that the grains from the up per course of the Zimnik Creek val ley sed i ments rep re sent what has eroded from the lo cal gold min er ali sa tion and this min er ali sa tion is prob a bly in the vi cin ity of the up stream sam pling site. The bi modal chem i cal com po si tion of the Au-Ag-Pd-Hg al loy grains with electrum and me dium-Ag grains (<15 wt.% Ag) found in the study area is typ i cal of the Rote Fäule and Kupferschiefer-re lated gold min er ali sa tion on the south ern side of the North Sudetic Trough and the Sieroszowice-Polkowice cop per min ing dis trict of the Fore-Sudetic Monocline. The study of the Ag con tents of placer grains from the Zimnik Creek drain age ba sin high lights the con trast be tween the placer gold grains de rived from Paleozoic orogenic gold min er ali sa tion in the Sudetes (typ i cally sim ple Au-Ag al loys con tain ing be tween 5 and 20 wt.% of Ag) and the one formed by the ox i diz ing chlo ride hy dro ther mal sys tems. The grains iden ti fied in this man ner as orig i nat ing from the ox idiz ing hy dro ther mal sys tem of the tran si tional zone can be dis tin guished from the placer gold de rived from other styles of min er ali sa tion, which are not Rote Fäule-re lated. It is par tic u larly im por tant con sid er ing the on go ing re con nais sance ex plora tion in the North Sudetic Trough (SW Po land), which em ploys gold grain anal y ses as a pros pect ing tool for the de tec tion of po ten tial...

Chemical and mineralogical characteristics and origin of placer gold from fluvial deposits of Żeliszowski Creek (North Sudetic Basin, SW Poland)

“…4). In struc ture and el emen tal dis tri bu tion this 150 µm par ti cle is sim i lar to the bi modal gold grains dis tin guished by Wierchowiec and Zieliñski (2017). The core of the grain is com posed of a metastable phase, while the rim is com posed of a na tive gold phase, of ten po rous; the con tact be tween the phases is al ways sharp.…”

“…The pres ence of mer cury as well as the Z-8 grain's pris tine shape are in di ca tors of its brief trans port. Ac cord ing to Wierchowiec and Zieliñski (2017), mercury oc cur rence within gold min er als in di cates a late, epi thermal stage of their crys tal li za tion in the source rock. The Au-Ag amal gams were formed by the recrystallization of the orig i nal Au-Ag-Pd min er als un der the in flu ence of low-tem per a ture Hg-bear ing so lu tions.…”

“…Both the chem i cal com po si tion of the gold grains and the min er al og i cal com po si tion of the microinclusions in di cate a likely con nec tion be tween the de tri tal gold oc cur rences of the The multiphase amal gams from the ¯eliszowski and the Jamna Creeks (Kania and Muszer, 2017;Kania, 2018) and the bi modal gold par ti cles from the vi cin ity of Grodziec (Wierchowiec and Zieliñski, 2017) are char ac ter ized by a sim i -lar struc ture and phase com po si tion. The pres ence of mer cury as well as the Z-8 grain's pris tine shape are in di ca tors of its brief trans port.…”

“…This method is based on an out line de vel op ment in dex (K in dex), de fined as the re la tion of the length of a par tic u lar grain's out line to the length of cir cum fer ence of a cir cle of an area equal to that of the ana lysed grain (Kania, 2020). A gold grain mi grating in sed i ments is orig i nally ir reg u lar, and be comes pro gressively rounded (Hérail et al, 1990;DiLabio, 1991;Loen, 1995;Wierchowiec, 2002;Kelley et al, 2003;Townley et al, 2003). There fore, the re la tion be tween that grain's out line and the area of its cross-sec tion steadily de creases (Kania, 2020).…”

“…1. red-bed type Perm ian Cu-polymetallic for ma tion of the North Sudetic Ba sin (Urbañski, 2010;Muszer, 2011;Oszczepalski et al, 2011;Wierchowiec and Zieliñski, 2017;Kania, 2018); 2. quartz veins, mainly of the Kaczawa Meta mor phic Complex (Kania, 2018;Wierchowiec et al, 2021) and gran ite gneiss of the W¹dro¿e Mas sif (Grodzicki, 1966;Mikulski and Wierchowiec, 2013;Wierchowiec et al, 2018); 3. ad ja cent rocks of the Izera-Karkonosze Block (Grodzicki, 1963(Grodzicki, , 1969. Fur ther more, the lo cal gold-bear ing sands and peb bles may also be en riched in gold grains which orig i nally crys tal lized in the pri mary Au-polymetallic de pos its of Scan di na via (Jêczmyk and Krzemiñska, 1996;£uszczkiewicz and Muszer, 1999;Muszer, 2011).…”