Franz Michael Meyer, Franz Michael
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VEINS AND HYDROTHERMAL BRECCIAS OF THE RANDU KUNING PORPHYRY Cu-Au AND EPITHERMAL Au DEPOSITS AT SELOGIRI AREA, CENTRAL JAVA INDONESIA Sutarto, Sutarto; Idrus, Arifudin; Harijoko, Agung; Setijadji, Lucas Donny; Meyer, Franz Michael
Journal of Applied Geology Vol 7, No 2 (2015): Current Issue
Publisher : Geological Engineering Department Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.22146/jag.26982

Abstract

The Randu Kuning prospect is situated at Selogiri area, Wonogiri, Central Java, Indonesia. This location is about 40 km to the south-east from Solo city or approximately 70 km east of Yogyakarta city. Many Tertiary dioritic rocks related alterationmineralisation were found at the Randu Kuning area and its vicinity, including hornblende microdiorite, hornblende-pyroxene diorite and quartz diorite. Mineralisation type of the Randu Kuning prospect was interpreted as porphyry Cu-Au and a number epithermal Au-base metals deposits in its surrounding. The closed existing of porphyry Cu-Au and epithermal Au-base metals type deposits at the Randu Kuning area produced a very complex of veins and hydrothermal breccias crosscutting relationship. A lot of porphyry veins types were found and observed at the Randu Kuning area, and classified into at least seven types. Most of the porphyry veins were cross cut by epithermal type veins. Many epithermal veins also are found and crosscut into deeply porphyry vein types. There are genetically at least two type of hydrothermal breccias have recognized in the research area, i.e. magmatic-hydrothermal breccia and phreatomagmatic breccia. Magmatic hydrothermal breccias are mostly occured in contact between hornblende microdiorite or quartz diorite and hornblende-pyroxene diorite, characterized by angular fragments/clasts supported or infilled by silicas, carbonates and sulphides matrix derived from hydrothermal fluids precipitation. Phreatomagmatic breccias are characterized by abundant of the juvenile clasts, indicated contact between hot magma with fluid or water as well as many wall rock fragments such as altered diorites and volcaniclastic rock clasts set in clastical matrix. The juvenile clasts usually compossed by volcanic glasses and aphanitic rocks in rounded-irregular shape. Both veining and brecciation processes have an important role in gold and copper mineralisation of the Randu Kuning Porphyry Cu-Au and epithermal Au-base metals deposits, mostly related to the presence of quartz veins/veinlets containing significant sulphides, i.e., quartz with thin centre line sulphides (Abtype) veins, pyrite±chalcopyrite (C type) veinlets, pyrite+quartz± chalcopyrire±carbonate (D type) veins of porphyry types as well as epithermal environment quarts+ sulphides+carbonate veins.
THE METAMORPHIC ROCK-HOSTED GOLD MINERALIZATION AT BOMBANA, SOUTHEAST SULAWESI: A NEW EXPLORATION TARGET IN INDONESIA Idrus, Arifudin; Fadlin, Fadlin; Prihatmoko, Sukmandaru; Warmada, I Wayan; Nur, Irzal; Meyer, Franz Michael
Jurnal Geologi dan Sumberdaya Mineral Vol 22, No 1 (2012): Jurnal Sumber Daya Geologi
Publisher : Pusat Survei Geologi

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (533.652 KB)

Abstract

Placer gold has been discovered in Bombana, SE-Sulawesi, Indonesia. The placer gold is not associated with volcanic rock-related gold deposits. This paper discusses the primary gold mineralization as the source of the placer gold. The placer gold is possibly derived from gold-bearing quartz veins hosted by Pompangeo Metamorphic Complex (PMC). Pyrite, chalcopyrite, cinnabar, stibnite and tripuhyite are present. Sheared, segmented vein varies in thickness from 2 cm to 2 m. The veins contain erratic gold in various grades from below detection limit (0.005 g/t) to 134 g/t. At least three generations of veins are identified. The first is parallel to the foliations, the second crosscuts the first generation of veins/foliations, and the third is of laminated deformed quartz+calcite veins at the late stage. The first veins are mostly massive to crystalline, occasionally brecciated and sigmoidal, whereas the second veins are narrower than the first and relatively brecciated. Gold grades in the second and third veins are relatively higher than that in first veins. Fluid inclusion study of quartz veins indicates abundant H2O-NaCl and a small amount of H2O-NaCl-CO2 inclusions. Temperature of homogenization (Th) and salinity of the first vein vary from 184.7 to 245.3 ºC and 5.26 to 9.08 wt.% NaCl eq., respectively. The second generation vein was originated at Th of 132.1-283.4 ºC and salinity of 3.55-5.86 wt.%NaCl eq., whereas the third generation vein formed at lowest Th varying from 114 to 176ºC and less saline fluid at salinity range between 0.35 and 4.03 wt.% NaCl eq. Gold is mainly identified in the form of 'free gold' among silicate minerals. Mineralogically, gold is closely related to cinnabar, stibnite, tripuhyite and possibly minor arsenopyrite. Metamorphogenic gold deposits would be the new target of gold exploration in Indonesia.Keyword: Gold mineralization, orogenic-type, Bombana, Southeast Sulawesi, Indonesia
GEOLOGY AND ORE MINERALISATION OF NEOGENE SEDIMENTARY ROCK HOSTED LS EPITHERMAL GOLD DEPOSIT AT PANINGKABAN, BANYUMAS REGENCY, CENTRAL JAVA, INDONESIA Idrus, Arifudin; Hakim, Fahmi; Warmada, I Wayan; Aziz, Mochammad; Kolb, Jochen; Meyer, Franz Michael
Journal of Applied Geology Vol 7, No 2 (2015): Current Issue
Publisher : Geological Engineering Department Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.22146/jag.26981

Abstract

Low suphidation (LS) epithermal gold deposits were recently found in the Paningkaban area, Central Java province, Indonesia, with more than five hundred artisanal gold miners currently operating in the area. This study is aimed to understand the geological factors controlling the gold mineralization and to characterize the alteration and ore mineralogy of the deposit. Several epithermal veins/veinlets trending N–S, NW–SE, and NE–SW are hosted by Tertiary turbiditic volcanoclastic sedimentary rocks of the Halang formation. This formation is composed of looping gradation of sandstone and siltstone units. Pre- and syn-mineralization structures such as extension joints, normal sinitral fault and sinitral fault control the gold mineralization. Fault movements formed dilational jogs manifested by NW-SE-trending en-echelon tension gash veins. Four main alteration zones are identified: (a) phyllic, (b) argillic, (c) sub propylitic and (d) weak subpropylitic. Ore minerals consist of native gold, electrum, native silver, pyrite, chalcopyrite, sphalerite, galena, arsenopyrite, cubanite, marcasite, covellite and tennantite, which are commonly associated withargillic alteration. Vein structures such as massive, swarm and low angle veins, stockwork and veins dispersed in diatreme breccia are present. Normal banded, cockade, crustiform, bladed carbonates as well as, comb and saccharoidal features are the typical vein textures. It is noteworthy that the veins are basically composed of carbonate with minor quartz at gold grades of up to 83 g/t Au. Based on the vein structures and textures, four stages of ore mineralization were developed consisting of (a) early stage (fluidized breccia and quartz vein), (b) middle stage (carbonate base metal), (c) late stage (late carbonate), and supergene stage. Gold mineralization originated mainly during middle and late stages, particularly in association with cockade, crustiform, bladed carbonate base metal veins. Based on those various features, the LS epithermal deposit in the study area is categorized as carbonate-base metalgold mineralization type.
Hydrothermal Alteration and Mineralization of the Randu Kuning Porphyry Cu-Au and Intermediate Sulphidation Epithermal Au-Base Metals Deposits in Selogiri, Central Java, Indonesia Sutarto, Sutarto; Idrus, Arifudin; Harijoko, Agung; Setijadji, Lucas Donny; Meyer, Franz Michael; Sindern, Sven; Putranto, Sapto
Journal of Applied Geology Vol 1, No 1 (2016)
Publisher : Geological Engineering Department Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.22146/jag.26951

Abstract

The Randu Kuning Porphyry Cu-Au prospect area is situated in the Selogiri district, Wonogiri regency, Central Java, Indonesia, about 40 km to the South-East from Solo city, or approximately 70 km east of Yogyakarta city. The Randu Kuning area and its vicinity is a part of the East Java Southern Mountain Zone, mostly occupied by both plutonic and volcanic igneous rocks, volcaniclastic, silisiclastic and carbonate rocks. Magmatism-volcanism products were indicated by the abundant of igneous and volcaniclastic rocks of Mandalika and Semilir Formation. The Alteration zones distribution are generally controlled by the NE–SW and NW–SE trending structures. At least eight types of hydrothermal alteration at the Randu Kuning area and its vicinity had been identified, i.e. magnetite + biotite ± K-feldspar ± chlorite (potassic), chlorite + sericite + magnetite ± actinolite, chlorite + magnetite ± actinolite ± carbonate (inner propylitic), chlorite + epidote ± carbonate (outer propylitic), sericite + quartz + pyrite (phyllic), illite + kaolinite ± smectite (intermediate argillic), illite + kaolinite ± pyrophyllite ± alunite (advanced argillic) and quatz + chlorite (sillisic) zones. The Randu Kuning mineralization at Selogiri is co existing with the porphyry Cu-Au and intermediate sulphidation epithermal Au-base metals. Mineralization in the porphyry environment is mostly associated with the present of quartz-sulphides veins including AB, C, carbonate-sulphides veins (D vein) as well as disseminated sulphides. While in the epithermal prospect, mineralization is particularly associated with pyrite + sphalerite + chalcopyrite + carbonate ± galena veins as well as hydrothermal breccias. The Randu Kuning porphyry prospect has copper gold grade in range at about 0.66–5.7 gr/t Au and 0.04–1.24 % Cu, whereas in the intermediate sulphidation epithermal contain around 0.1–20.8 gr/t Au, 1.2–28.1 gr/t Ag, 0.05–0.9 % Zn, 0.14–0.59 % Pb and 0.01–0.65 % Cu.
Metamorphic rock-hosted orogenic gold deposit style at Bombana (Southeast Sulawesi) and Buru Island (Maluku): Their key features and significances for gold exploration in Eastern Indonesia Idrus, Arifudin; Prihatmoko, Sukamandaru; Harjanto, Ernowo; Meyer, Franz Michael; Nur, Irzal; Widodo, Wahyu; Agung, Lia Novelia
Journal of Geoscience, Engineering, Environment, and Technology Vol 2 No 2 (2017): JGEET Vol 02 No 02 : June (2017)
Publisher : UIR PRESS

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24273/jgeet.2017.2.2.291

Abstract

In Indonesia, gold is commonly mined from epithermal-, porphyry-, and skarn-type deposits that are commonly found in volcanic belts along island arcs or active continental margin settings. Numerous gold prospects, however, were recently discovered in association with metamorphic rocks. This paper focuses on metamorphic rock-hosted gold mineralization in Eastern Indonesia, in particular the Bombana (SE Sulawesi) and Buru Island (Maluku) prospects. At Bombana, gold-bearing quartz-veins are hosted by the Pompangeo metamorphic complex. Sheared, segmented veins vary in thickness from 2 cm to 2 m. Gold is mainly present in the form of ‘free gold’ among silicate minerals and closely related to cinnabar, stibnite, tripuhyite, and in places, minor arsenopyrite. The gold distribution is erratic, however, ranging from below detection limit up to 134 g/t. At least three generations of veins are identified. The first is parallel to the foliation, the second crosscuts the first generation of veins as well as the foliation, and the late-stage laminated deformed quartz-calcite vein represents the third mineralization stage. The early veins are mostly massive to crystalline, occasionally brecciated, and sigmoidal, whereas the second-stage veins are narrower than the first ones and less subjected to brecciation. Gold grades in the second- and third-stage veins are on average higher than that in the earlier veins. Microthermometric and Raman spectrometric studies of fluid inclusions indicate abundant H2O-NaCl and minor H2O-NaCl-CO2 fluids. Homogenization temperatures and salinities vary from 114 to 283 ºC and 0.35 to 9.08 wt.% NaCl eq., respectively. Crush-leach analysis of fluid inclusions suggests that the halogen fluid chemistry is not identical to sea water, magmatic or epithermal related fluids, but tends to be similar to fluids in mesothermal-type gold deposits. In Buru Island (Gunung Botak and Gogorea prospects), two distinct generations of quartz veins are identified. Early quartz veins are segmented, sigmoidal discontinuous and parallel to the foliation of the host rock. This generation of quartz veins is characterized by crystalline relatively clear quartz, and weakly mineralized with low sulfide and gold contents. The second type of quartz veins occurs within the ‘mineralized zone’ of about 100 m in width and ~1,000 m in length. Gold mineralization is intensely overprinted by argillic alteration. The mineralization-alteration zone is probably parallel to the mica schist foliation and strongly controlled by N-S or NE-SW-trending structures. Gold-bearing quartz veins are characterized by banded texture particularly following host rock foliation and sulphide banding, brecciated and rare bladed-like texture. Alteration types consist of propylitic (chlorite, calcite, sericite), argillic and carbonation represented by graphite banding and carbon flakes. Ore mineral comprises pyrite, native gold, pyrrhotite, and arsenopyrite. Cinnabar and stibnite are present in association with gold. Ore chemistry indicates that 11 out of 15 samples yielded more than 1 g/t Au, in which 6 of them graded in excess of 3 g/t Au. All high-grade samples are composed of limonite or partly contain limonitic material. This suggests the process of supergene enrichment. Interestingly, most of the high-grade samples contain also high concentrations of As (up to 991ppm), Sb (up to 885ppm), and Hg (up to 75ppm). Fluid inclusions in both quartz vein types consist of 4 phases including L-rich, V-rich, L-V-rich and L1-L2-V (CO2)-rich phases. The mineralizing hydrothermal fluid typically is CO2-rich, of moderate temperature (300-400 ºC), and low salinity (0.36 to 0.54 wt.% NaCl eq). Based on those key features, gold mineralization in Bombana and Buru Island tends to meet the characteristics of orogenic, mesothermal types of gold deposit. Metamorphic rock-hosted gold deposits could represent the new targets for gold exploration particularly in Eastern Indonesia.
METAMORPHIC ROCK-HOSTED OROGENIC GOLD DEPOSIT STYLE AT BOMBANA (SOUTHEAST SULAWESI) AND BURU ISLAND (MALUKU): THEIR KEY FEATURES AND SIGNIFICANCES FOR GOLD EXPLORATION IN EASTERN INDONESIA Idrus, Arifudin; Prihatmoko, Sukamandaru; Harjanto, Ernowo; Meyer, Franz Michael; Nur, Irzal; Widodo, Wahyu; Agung, Lia Novelia
Journal of Geoscience, Engineering, Environment, and Technology Vol. 2 No. 2 (2017): JGEET Vol 02 No 02 : June (2017)
Publisher : UIR PRESS

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.24273/jgeet.2017.2.2.291

Abstract

In Indonesia, gold is commonly mined from epithermal-, porphyry-, and skarn-type deposits that are commonly found in volcanic belts along island arcs or active continental margin settings. Numerous gold prospects, however, were recently discovered in association with metamorphic rocks. This paper focuses on metamorphic rock-hosted gold mineralization in Eastern Indonesia, in particular the Bombana (SE Sulawesi) and Buru Island (Maluku) prospects. At Bombana, gold-bearing quartz-veins are hosted by the Pompangeo metamorphic complex. Sheared, segmented veins vary in thickness from 2 cm to 2 m. Gold is mainly present in the form of ?free gold? among silicate minerals and closely related to cinnabar, stibnite, tripuhyite, and in places, minor arsenopyrite. The gold distribution is erratic, however, ranging from below detection limit up to 134 g/t. At least three generations of veins are identified. The first is parallel to the foliation, the second crosscuts the first generation of veins as well as the foliation, and the late-stage laminated deformed quartz-calcite vein represents the third mineralization stage. The early veins are mostly massive to crystalline, occasionally brecciated, and sigmoidal, whereas the second-stage veins are narrower than the first ones and less subjected to brecciation. Gold grades in the second- and third-stage veins are on average higher than that in the earlier veins. Microthermometric and Raman spectrometric studies of fluid inclusions indicate abundant H2O-NaCl and minor H2O-NaCl-CO2 fluids. Homogenization temperatures and salinities vary from 114 to 283 ºC and 0.35 to 9.08 wt.% NaCl eq., respectively. Crush-leach analysis of fluid inclusions suggests that the halogen fluid chemistry is not identical to sea water, magmatic or epithermal related fluids, but tends to be similar to fluids in mesothermal-type gold deposits. In Buru Island (Gunung Botak and Gogorea prospects), two distinct generations of quartz veins are identified. Early quartz veins are segmented, sigmoidal discontinuous and parallel to the foliation of the host rock. This generation of quartz veins is characterized by crystalline relatively clear quartz, and weakly mineralized with low sulfide and gold contents. The second type of quartz veins occurs within the ?mineralized zone? of about 100 m in width and ~1,000 m in length. Gold mineralization is intensely overprinted by argillic alteration. The mineralization-alteration zone is probably parallel to the mica schist foliation and strongly controlled by N-S or NE-SW-trending structures. Gold-bearing quartz veins are characterized by banded texture particularly following host rock foliation and sulphide banding, brecciated and rare bladed-like texture. Alteration types consist of propylitic (chlorite, calcite, sericite), argillic and carbonation represented by graphite banding and carbon flakes. Ore mineral comprises pyrite, native gold, pyrrhotite, and arsenopyrite. Cinnabar and stibnite are present in association with gold. Ore chemistry indicates that 11 out of 15 samples yielded more than 1 g/t Au, in which 6 of them graded in excess of 3 g/t Au. All high-grade samples are composed of limonite or partly contain limonitic material. This suggests the process of supergene enrichment. Interestingly, most of the high-grade samples contain also high concentrations of As (up to 991ppm), Sb (up to 885ppm), and Hg (up to 75ppm). Fluid inclusions in both quartz vein types consist of 4 phases including L-rich, V-rich, L-V-rich and L1-L2-V (CO2)-rich phases. The mineralizing hydrothermal fluid typically is CO2-rich, of moderate temperature (300-400 ºC), and low salinity (0.36 to 0.54 wt.% NaCl eq). Based on those key features, gold mineralization in Bombana and Buru Island tends to meet the characteristics of orogenic, mesothermal types of gold deposit. Metamorphic rock-hosted gold deposits could represent the new targets for gold exploration particularly in Eastern Indonesia.