High Sulphidation Research Articles

An APS mineralization in the kaolin deposit Desa Toraget from northern Sulawesi, Indonesia

Two different types of APS minerals are described for the first time from the Desa Toraget kaolin deposit (Sulawesi, Indonesia). Type I is a near end member alunite with some PO 4 3− substituting for (SO 4) 2−. The second type contains Ca at a maximum of 0.28 in the structural formula and as a consequence of this, phosphate (−0.47) increased at the expense of SO 4 2− (1.53). The compositional data attest to a solid solution between woodhouseite and pure alunite. Desa Toraget kaolin mineralization, hence may be classified as “advanced argillic alteration” which requires high oxidation and sulfidation and is related in time and space to the Quaternary volcanic activity. In view of the genetic linkage between epithermal Au mineralization and high sulphidation kaolinitic alteration elsewhere, the study area might be considered as a potential target for Au exploration.

The Enåsen gold deposit, central Sweden

Stable isotope analyses of quartz, sulphides, and magnetite were conducted to provide information on thermal history and source of hydrothermal fluids in the Palaeoproterozoic Enasen gold deposit. Reequilibration and homogenization of oxygen isotopes throughout the rock have apparently not occurred despite the upper amphibolite to granulite facies regional metamorphism that has affected the rocks. However, oxygen isotope geothermometry on a coexisting quartz-magnetite pair gave a minimum temperature for peak metamorphism of around 650 °C which agrees with Fe-Mg geothermometry. This suggests that grain-scale equilibrium is achieved. The variation in oxygen isotope ratios (δ18O = 7.3 – 10.5‰) on quartz from the metamorphosed acid sulphate alteration zone is suggested to represent a cooling trend in the fossil hydrothermal system with higher δ18O-values in more superficial parts. Temperatures of alteration and silicification and isotopic composition of hydrothermal fluids could not be defined from the present data but it was recognized that the data is compatible with a epithermal genesis for the deposit. It is suggested that alteration, silicification, and mineralization at the Enasen gold deposit took place in a high sulphidation epithermal environment at temperatures of around 200–250 °C and that the hydrothermal fluids consisted of meteoric and magmatic water. A tentative reconstruction of the fossil hydrothermal system is presented. Sulphur isotope ratios of sulphides from the fold-bearing quartz-sillimanite gneiss gave δ34S-values close to zero indicating a magmatic source of the sulphur.

High Temperature Oxidation and Sulphidation and Its Prevention by Ceramic Coatings

High Temperature Oxidation and Sulphidation and Its Prevention by Ceramic Coatings

Magmatic arcs and associated gold and copper mineralization in Indonesia

Gold mineralization in Indonesia formed in andesitic arcs which were active for intervals of between 3 and 20 My from the Cretaceous to Pliocene. Fifteen major arcs are identified with a total on land extent of over 15,000 kms. Known orebodies and major prospects are confined to six arcs within the mid-Tertiary to Pliocene age range. In Indonesia, these arcs total approximately 7,000 kms in length and contain combined historical production and current resources in excess of 2,500 tonnes of gold and 20 million tonnes of copper. Individual arcs or segments of arcs are characterized by specific types of mineralization reflecting both arc basement related to earlier collisions and reversals in tectonic polarity, and erosion level. Porphyry copper-gold, skarn, and high sulphidation enargite-gold deposits formed in both island arc and continental settings where intrusive stocks ascended to shallow depths near the base of a coeval volcanic sequence. Low sulphidation epithermal deposits, largely confined to the western Sunda-Banda and Central Kalimantan continental arcs, formed preferentially in the lower part of the volcanic pile and sometimes at the basement surface. The low sulphidation deposits may be underlain at depths of several kilometres by sills which provided heat for the hydrothermal systems; the deposits probably formed during late-stage extension on low-angle faults. Sediment-hosted mineralization developed where low sulphidation fluids encountered favourable calcareous marine sedimentary rocks at epithermal depths. The distinctive gold-silver-barite±base metal deposits of eastern Indonesia may have formed by venting of high sulphidation fluids into restricted shallow marine basins. As more information becomes available and understanding of arc systems increases, the proposed relationships of deposit type to upper basement and stage of arc evolution, and deposit abundance to erosion level, are likely to become increasingly useful to regional and district scale assessments of mineral potential, both in Indonesia and in arc environments elsewhere.

Evaluation of high temperature sulphidation protection provided by amorphous Si/SiO2 coatings produced by ArF excimer laser chemical vapour deposition

Evaluation of high temperature sulphidation protection provided by amorphous Si/SiO2 coatings produced by ArF excimer laser chemical vapour deposition

Geological setting and styles of mineralization, north arm of Sulawesi, Indonesia

The north arm of Sulawesi consists of a Neogene island arc (North Sulawesi Arc) built upon Paleogene volcanic-sedimentary basement and underlain by oceanic crust, which is followed to the west by an arcuate, highly deformed terrane (neck of Sulawesi) characterized by metamorphic rocks and felsic granitoids belonging to the Sundaland continental margin. These two terranes have been contiguous during the Tertiary. The evolution of the North Sulawesi Arc is divided into two stages separated by collision of the north arm with the Sula Platform microcontinent in mid-Miocene time. During the Early Miocene a calc-alkaline andesitic arc developed in relation to west-directed subduction. Arc-continent collision resulted in back-arc thrusting, clockwise rotation of the north arm, and inception of subduction along the North Sulawesi Trench. Post-collisional magmatism in the North Sulawesi Arc produced felsic to mafic volcanic suites that are thought to be related primarily to rifting of the former arc rather than directly to subduction. In the neck of Sulawesi,LILE and LREE-element enriched, potassic granites (Dondo suite) of continental affinity (Sr 87/Sr 86 0.71) were generated. The north arm of Sulawesi is comparatively well mineralized. Porphyry CuAu and porphyry Mo mineralization is approximately 2–4 Ma old based on preliminary KAr dating and geological relationships. The former developed in an oceanic terrane following collision-related arc reversal, whereas the latter developed in a continental terrane that underwent lower crustal melting during extension following the same collision. Porphyry CuAu mineralization in the North Sulawesi Arc is associatedwith clusters of small hornblende diorite or quartz diorite stocks, but the specific volcanic environment above these intrusions and their magmatic affinity remain unknown. Mineralization related to porphyry CuAu districts includes CuAu skarn, polymetallic vein and high sulphidation epithermal Au (+enargite). Porphyry Mo mineralization in the neck of Sulawesi is related to small stocks or roof apophyses of the Dondo batholith. Cogenetic granites are exposed over 5000 km 2 and are intruded in an arcuate belt, more than 400 km long, parallel to the Sula Platform collision zone. Unimodal felsic volcanics of Plio-Pleistocene age, which occur locally along the inner side of the north arm and further to the south, are probably the extrusive equivalents of the Dondo granites. Epithermal Au mineralization (typically quartz-calcite veins ± adularia) is associated mainly with the Early Miocene andesitic arc but there are important exceptions, and in general the age of mineralization is poorly known. A district-wide correlation between epithermal Au mineralization and porphyry CuAu mineralization is not apparent. The most important epithermal Au district (Kotamobagu) is inferred to be associated with a long-lived volcanic center represented by the Moat caldera. Epithermal gold systems in the North Sulawesi Arc are generally eroded deeply, typically with chlorite-epidote wallrock alteration, and little is known about their associated volcanic environment. In addition to high sulphidation Au mineralization related to porphyry systems, other styles and settings of Au mineralization in the north arm are exemplified by the Gunung Pani rhyolitic dome, the Patung diatreme breccia, the Mesel jasperiod, hosted partly by carbonate rocks, and sedimentary replacement Au-base metal mineralization at Doup. Diversity of mineralization in the north arm is further illustrated by VMS mineralization in volcanic basement to the Neogene arc, and by metamorphogenic quartz vein Au mineralization in the neck of Sulawesi.

High temperature oxidation and sulphidation and their prevention by ceramic coatings

AbstractA survey is presented of the research on high temperature oxidation and sulphidation conducted in the author's laboratory. The importance of the effects of high temperature corrosion are reviewed and the principal methods of preventing it are discussed. The production, properties, and testing of thin ceramic coatings as a means of protecting metals against aggressive atmospheres at high temperatures are then considered in greater detail. Finally, some directions for future research are suggested.

High temperature oxidation and sulphidation and their prevention by ceramic coatings

High temperature oxidation and sulphidation and their prevention by ceramic coatings

Polyborane-derived metal borides. 1. Hydrodesulphurization catalysts with potential for coal liquefaction

A new class of metal borides prepared at elevated temperatures and under hydrogen pressure from borane anions and cobalt or nickel salts catalyse the hydrodesulphurization of thiophene at 400 °C to butane and H 2S. The most active catalysts are prepared from the anions NaB 5H 8 and NaB 10H 13. These borides have unusually high boron levels (12–17%) and exhibit high sulphidation resistances. Using these catalysts, 88–99% conversion of thiophene is observed. With less active catalyst systems or at lower temperatures, butene and tetrahydrothiophene are also produced. Under similar reaction conditions, the nickel-pentaborane derived catalyst promotes 93% hydrogenolysis of furan. The boride catalysts do not promote hydrogenation of non-heterocyclic aromatics such as toluene and ethylbenzene. The potential of these new boride systems in processes related to coal liquefaction is discussed.