Ore‐forming physicochemical conditions of tellurium–gold deposits: A case study from the Guilaizhuang deposit, eastern North China

Abstract

Tellurium–gold deposits differ from normal gold mineralization in their significant content of tellurium‐bearing minerals with a close relation between Au and Te. The Guilaizhuang gold deposit is a major tellurium–gold deposit in the Shandong Province of China, and is located in the eastern margin of the North China Craton. The main sulfide minerals in this deposit are pyrite, As‐bearing pyrite, arsenopyrite, chalcopyrite, galena, sphalerite, chalcocite, and argentite. Tellurides contain native tellurium, altaite, coloradoite, petzite, and calaverite. Here, we investigate the fluid characteristics based on fluid inclusion studies and evaluate the intensive variables through thermodynamic computations to evaluate the ore genesis. We identify four stages for the mineralization: quartz‐pyrite stage, gold‐polymetallic sulfide stage, gold‐telluride stage, and carbonate stage. The gold‐telluride stage represents the main stage of gold precipitation. In gold‐polymetallic sulfide stage, Au formed within pyrite and As‐bearing pyrite in the form of invisible gold, whereas in the gold‐telluride stage, Au occurs as visible gold, such as native gold, electrum, calaverite, and petzite. Our data show that the mineralizing fluids were partly acidic and reduced during the gold‐polymetallic sulfide stage. Gold was transported as AuCl2− and Au(HS)2− complexes which was reduced by Fe2+. Gold might also occur as submicroscopic Au0 inclusions in pyrite and As‐bearing pyrite. The acidic state of the fluids favoured Au leaching from the surrounding rocks. During the gold‐telluride stage, gold might have migrated mostly as Au(HTe)2− and the Te combined at first with Ag to form hessite and subsequently with Au and Ag to form petzite and calaverite. With the decrease in Te content and increase in Au saturation, tellurium and native gold were precipitated. Our study provides insights into the physicochemical conditions of the formation of Te–Au deposits.

In–Situ LA-ICP-MS Trace Elements Analysis of Pyrite and the Physicochemical Conditions of Telluride Formation at the Baiyun Gold Deposit, North East China: Implications for Gold Distribution and Deposition

“…It is predicted that there are not easily formed under conditions of high sulfur fugacity, that is, a large amount of sulfide precipitation. Similar phenomena have also been found in other tellurium-gold deposits in NCC [19,46,53]. Another possibility is the loss of telluride due to the lack of Te in the early ore-forming fluid.…”

“…The Baiyun gold deposit is the second largest gold deposit in the district (the proven reserves are 31.7 t with an average grade of 2.85 g/t, The Bureau of Non-Ferrous Geology of Liaoning Province 103 Team, 2015). However, the origin of the deposit, the age of mineralization and the origin of the ore-forming fluids remain in controversial [17][18][19][20][21][22][23][24].…”