17:15 〜 19:15
[HRE12-P01] Petrography and geochemical characteristics of the Gudang Handak veins in the Pongkor epithermal Au-Ag deposit, Indonesia
キーワード：Low sulphidation epithermal system, Pongkor Au-Ag Deposit, Indonesia, Quartz textures, ICP-OES/MS analysis, SEM-EDS/EPMA analysis
The Pongkor deposit is a low-sulfidation type epithermal gold-silver deposit located in the Bogor District, West Java, Indonesia. The Pongkor mine has been in operation since 1994, with four vein groups being exploited to date. The operation has been conducted at mining levels between 435 and 700 masl. The production of the Gudang Handak (GH) vein group has been conducted at the deepest level in the deposit, 435 - 490 masl. The vein group consists mainly of 8 veins. Objective of this study is to reveal the characteristics of mineralization of the Gudang Handak vein group, especially between the GH-B vein and the GH-C vein where the mining activities are being conducted. Methods employed include petrography, X-ray diffraction (XRD), X-ray fluorescent (XRF), inductively coupled plasma optical emission spectroscopy/mass spectroscopy (ICP-OES/MS), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), and electron probe micro analyser (EPMA).
On the basis of the petrography, the GH-B veins observed at 435 masl is 2 m wide and consists of flamboyant, microcrystalline, feathery, colloform, comb, and granular quartz, and bladed calcite. The GH-B vein observed at 450 masl is 2 m wide and consists of microcrystalline, ghost sphere, comb, crustiform, and flamboyant quartz, bladed calcite, and rhombic adularia. The GH-B vein observed at 460 masl is 2 m wide and consists of flamboyant and microcrystalline quartz and granular calcite. The GH-B vein observed at 490 masl is 3 wide and consists of microcrystalline, flamboyant, mosaic, and granular quartz, granular rhodochrosite, as well as bladed and granular calcite. The GH-C vein observed at 490 masl is 2 m wide consists of flamboyant, microcrystalline, colloform, and granular quartz and granular calcite. The microcrystalline quartz is most commonly associated with Au-Ag minerals. Ore minerals in all the veins observed are electrum, aguilarite, pyrite, and sphalerite.
Bulk chemical compositions of the veins show that Au has positive correlations with Ag and Se. The GH-B vein has 0.31-56.0 g/t Au (av. 9.67 g/t Au) and 0.02-655 g/t Ag (av. 133 g/t Ag), and the GH-C vein has 0.04-22.7 g/t Au (av. 5.33 g/t Au) and 0.02-422 g/t Ag (av. 77.5 g/t Ag). The average Ag/Au ratios of the GH-B and GH-C veins are 13.7 and 14.6, respectively. On the basis of mineral chemistry, the microcrystalline quartz in the GH-B and GH-C veins has a positive correlation between Al and K. Ranges of Ag/(Au+Ag) atomic ratio of electrum in the GH-B and GH-C veins are 51-57 at. % and 53-59 at. %, respectively.
On the basis of the petrography, the GH-B veins observed at 435 masl is 2 m wide and consists of flamboyant, microcrystalline, feathery, colloform, comb, and granular quartz, and bladed calcite. The GH-B vein observed at 450 masl is 2 m wide and consists of microcrystalline, ghost sphere, comb, crustiform, and flamboyant quartz, bladed calcite, and rhombic adularia. The GH-B vein observed at 460 masl is 2 m wide and consists of flamboyant and microcrystalline quartz and granular calcite. The GH-B vein observed at 490 masl is 3 wide and consists of microcrystalline, flamboyant, mosaic, and granular quartz, granular rhodochrosite, as well as bladed and granular calcite. The GH-C vein observed at 490 masl is 2 m wide consists of flamboyant, microcrystalline, colloform, and granular quartz and granular calcite. The microcrystalline quartz is most commonly associated with Au-Ag minerals. Ore minerals in all the veins observed are electrum, aguilarite, pyrite, and sphalerite.
Bulk chemical compositions of the veins show that Au has positive correlations with Ag and Se. The GH-B vein has 0.31-56.0 g/t Au (av. 9.67 g/t Au) and 0.02-655 g/t Ag (av. 133 g/t Ag), and the GH-C vein has 0.04-22.7 g/t Au (av. 5.33 g/t Au) and 0.02-422 g/t Ag (av. 77.5 g/t Ag). The average Ag/Au ratios of the GH-B and GH-C veins are 13.7 and 14.6, respectively. On the basis of mineral chemistry, the microcrystalline quartz in the GH-B and GH-C veins has a positive correlation between Al and K. Ranges of Ag/(Au+Ag) atomic ratio of electrum in the GH-B and GH-C veins are 51-57 at. % and 53-59 at. %, respectively.