From 22 March to 24 March 2015 an AusIMM technical tour visited two underground gold mines in Guizhou province in the southwest of China.
Fifteen people took part in the tour, which visited two mines owned by Eldorado Gold: Jinfeng Mine and Shuiyindong Mine, to see Carlin-style sediment hosted gold mineralisation.
On day one of the tour many of us flew from Hong Kong to Guiyang, and then drove four hours from Guiyang to Zhenfeng. The drive was on a new-looking six lane highway which forced its way through the mountainous landscape and was suspended by viaducts above the villages below and through the mountains via long tunnels.
We arrived in Zhenfeng where we were shown the ‘breasts of nature’ by our tour leader Xing-Chun Zhang who made us all feel very welcome. Zhenfeng was where we stayed for the next two nights.
On day two we set off first thing in the morning and drove three and a half hours on rural roads to Jinfeng Mine, located southwest of Zhenfeng. The roads had us winding up and down the mountains rather than spanning across them and through them as the roads of the previous day had.
Jinfeng mine, the Lannigou deposit, is a sediment-hosted gold deposit with Carlin-like characteristics. The host rocks are Triassic in age and comprise a folded sequence of calcareous sandstone and mudstone. Folds and faults record at least two periods of superimposed NE-SW phases of shortening that alternate with periods of extension, the last phase of which was likely associated with gold mineralisation. The main ore controls are broad fault zones that cut the initial phase of folds but were reactivated during the later fold and thrust event. Gold mineralisation is superimposed on this complex geology with higher grades developing at fault intersections and within favourable lithologic units. Mineralisation styles include carbonaceous clay breccia, fault gouge seams and styolitic shear veins, silicified wall rock, breccias and veins with illite-dolomite alteration, quartz-dolomite-orpiment veins and stockwork. Gold occurs in arsenic rims on fine-grained pyrite-marcasite with late arsenopyrite, arsenic-antimony minerals and cinnabar (Zhang and Xia, 2015, Excursion Guide for Technical Tour No.5: China’s Carlins-like Golden Triangle).
On arriving at the mine we were taken to the main viewing platform where we got a great panoramic view of the whole operation. Then went to the administration office where we received our personal protective equipment and a comprehensive safety induction.
After lunch we were split into two groups, one headed for underground and the other headed for a tour of the open pit and ore stock piles – as geologists love crawling over high grade ore stock piles! Then the groups swapped after two hours. Having visited underground mines in Australia, New Zealand and the United States I thought that the Jinfeng Mine was on par with these with respect to safety standards and signage – including a familiar sign asking what colour my urine was on the back of the toilet room door.
On the morning of day three we drove on very narrow and winding roads to Shuiyindong Mine, northwest of Zhenfeng. Shuiyindong was much more a boutique Chinese mine compared with Jinfeng. It was much smaller in size, and did not have an open pit.
The Shuiyindong deposit lies on the eastern limb of the Huijiabao anticline, which is cut by reverse faults. The deposit is hosted in Permian limestone with the sedimentary rocks in the district consisting of bioclastic limestone, siltstone, and argillite of Permian and Triassic age. Gold mineralization occurs mainly on the flanks of the anticline and is preferentially disseminated in bioclastic limestone and calcareous siltstone where the lower grade ore bodies are hosted in silicified, brecciated argillite and limestone. The country rocks are most typically affected by decarbonation, silicification, sulfidation and dolomitization. Sulfides in the deposit are mainly arsenian pyrite, arsenopyrite, and marcasite with minor orpiment, realgar, and stibnite. Gangue minerals include quartz, dolomite, calcite, and clay minerals (Zhang and Xia, 2015, Excursion Guide for Technical Tour No.5: China’s Carlins-like Golden Triangle). All gold is contained in refractory ores in which arsenian pyrite is the major host mineral.
On arrival at the mine we kitted up and headed underground on a single chairlift. When I first walked into the room housing the massive cable system with small metal chairs heading off into the big dark unknown I was a little unnerved. However, the chairlift was a much more pleasant experience that I thought it was going to be, as we were not suspended too far off the ground, and there were stairs either side.
We moved around the underground mine on foot. The height of the drives was not an issue for me, but the taller members of the group had to watch out for the overhead high voltage cables. We looked at the mineralisation and geology, watched the mine workers load ore carts, and looked at a stope that was being worked.
After another trip on the chairlift back to the surface we had lunch, looked at the high grade ore pile before driving back to Guiyang where the tour ended.
This technical tour provided an amazing opportunity to visit operating mines in China. The experience increased my understanding of the manner in which these mines operate in, and the cultural background to these Chinese mining operations. The technical tour was well organised, ran smoothly and increased my understanding of sediment-hosted Carlin-like gold deposits.