Acid Sulfate Type Research Articles

Палеопочвы кровли протерозойского фундамента территории Курской магнитной аномалии

This work represents the results of multidisciplinary study of paleosols from the weathered roof of Precambrian basement (Stary Oskol, Belgorod region). Shallow paleosols were developed from ferruginous shale and diagenetically modified weathering crust of ferruginous quartzite which led to its sideritization. At the studied location (quarry of the Stoilensky mining and processing plant) the age of weathering crust is pre-Devonian. Both rocks contain pyrite. Paleosols developed under similar primitive lithophytic vegetation. The studied paleosols are identified as in situ, biotic, of extreme pedogenesis. The trigger for their development was the pyritization. As a result, the chemical weathering prevailed under physical and biological ones. Both soils were attributed to acid-sulfate. Paleosols have not developed the continuous cover. The paleosols previously discovered in this area were developed from ferruginous quartzite and are also attributed to the acid-sulfate type. It seems that this soil type was widely distributed in the past.

Sulfur formation associated with coexisting sulfide minerals in the Kemp Caldera hydrothermal system, Scotia Sea

The Kemp Caldera is a submarine caldera located in the southernmost part of the intra-oceanic South Sandwich arc, Scotia Sea. The caldera comprises a unique hydrothermal system in which elemental sulfur (S0) coexists with sulfide minerals at unusually high pH-values (pH25 °C > 5). During the 2019 R/V Polarstern PS119 expedition, samples from the white smoker vent fields in the center of the caldera were recovered by a remotely operated vehicle. The sampling of elemental sulfur took place at the vent sites “Great Wall” and “Toxic Castle”, which are located < 80 m apart. At Great Wall, sulfur is fine-crystalline, while at Toxic Castle S0 occurs in liquid form, forming amorphous and globular structures. Here, tabular plates of covellite are found as inclusions in the quenched sulfur. The fluids from both sites have pH-values of about 5.4 to 5.7 (at 25 °C) and show a relatively wide temperature range from 63 to > 200 °C. The isotope values of sulfide and elemental sulfur range from 4.6 to 5.8 ‰, while sulfate concentrations at Great Wall are lower than in seawater.Elemental sulfur in submarine arc/back-arc systems is commonly believed to form by disproportionation of SO2. It generally shows negative δ34S values and precipitates from acid-sulfate type hydrothermal fluids with pH-values as low as < 1. This formation mechanism, however, cannot explain the high pH and low sulfate concentration of the Great Wall fluid alongside high δ34S values of elemental sulfur and massive sulfides found at Kemp. Instead, we suggest that S0 formation at Kemp Caldera can be attributed to synproportionation of SO2 and H2S. This formation mechanism is thermodynamically feasible but has not been demonstrated to actually take place in hydrothermal systems. The association of elemental sulfur with covellite is also uncommon, but not unexpected in magmatic-hydrothermal systems. The uncommonly high pH-value is likely responsible for the precipitation of the metal sulfides, which are unusual for known acid-sulfate systems studied to date. Our study shows that the geochemical behavior of sulfur in arc/back-arc hydrothermal systems is more diverse than previously recognized.

Петрография вторичных кварцитов месторождения Алкамерген (Павлодарская область)

This paper presents the results of studying the features of formation and mineral composition of secondary quartzites of the Alkamergen deposit (Pavlodar region) through mineralogical and petrographic studies of samples on an automated diffractometer. The hydrothermal-altered rocks of the deposit, which are represented by medium-temperature secondary quartzites of the alunite facies, have been studied. The results of the research made it possible to establish the genetic features of the formation of the Alkamergen deposit. In terms of rock composition and ore mineralization, this object is a typical representative of acid-sulfate type deposits.

Fluid geochemistry and isotope compositions to delineate physical processes in Wayang Windu geothermal reservoir, Indonesia

Wayang Windu geothermal field, which is situated in quaternary volcanic rock, has been delivering 227 MW of electricity and is planned to be developed in near future. Isotope and geochemistry study has been done to support understanding of the system. Samples were taken from thermal manifestations and production wells (two-phase and dry steam wells) to analyse its isotope and chemical compositions. Most of the hot springs are bicarbonate type and have neutral pH values, except for steam heated waters found near fumarolic fields, which are acid sulfate type waters. Deep brine fluids are of mature chloride type, while other deep dilute fluids are bicarbonate type indicates the existance of condensate layer. Solute and gas geothermometer calculation showed good agreement with measured temperature, i.e., 280–300 °C. However, gas-gas equilibria calculation showed increasing T and decreasing y (steam fraction) compare to previous study which indicates contribution form hotter source with high liquid saturation. Aside from different recharge area of thermal manifestation and production wells, the isotopes composition also shows physical processes in reservoir, i.e., adiabatic boiling, steam separation at different temperature (140–260 °C) and steam fraction (0.30–0.65), and also mixing process with meteoric water.

Hydrothermal system of the Kirishima volcanic area inferred from the chemical and isotopic composition of spring waters and fumarolic gases

The chemical and isotopic composition of hot spring waters and fumarolic gases from the Kirishima volcanic area were investigated in order to delineate the geochemical structure of the hydrothermal systems. There are active volcanoes, Iwoyama, Shinmoe and Ohachi locate in the area, and each of them has characteristic hydrothermal systems. At Iwoyama volcano, chloride-sulfate type waters are discharging from central part, and acid sulfate type waters are located on its north and west flanks. On the south west flank of Shinmoe volcano, CO 2 type waters are located. At a deep part on the west Sank of both volcanoes chloride type waters are distributed. This variety of different type of waters can be derived from differentiations of a hypothetical parent fluid. The chloride type water seems to be a liquid phase separated from the mixture of the parental fluid and ground water. The vapor phase separated from the liquid phase heats ground water and produces the sulfate type and the CO 2 type waters. In the hydrothermal systems beneath Iwoyama volcano, a parental fluid is differentiated to a chloride-sulfate type water and a H 2 S rich fumarolic gas. The parent fluid in the hydrothermal system of Shinmoe volcano seems to be depleted in sulfur species than the parental fluid for Iwoyama. Ohachi volcano has a faint fumarolic activity at the summit. The fumarolic gas losses most of water vapor prior to the discharge due to a conductive cooling and condensation of the vapor up to the summit. A model calculation evaluates the original composition of the fumarolic gas from Ohachi volcano. The original composition resembles to those of the fumarolic gases from the summit of Shinmoe volcano.

Epithermal Au and polymetallic mineralization in the Tulasu Basin, western Tianshan, NW China: Potential for the discovery of porphyry Cu[sbnd]Au deposits

The Tulasu basin is an important epithermal Au mineralization district in western Tianshan in northwestern China. Geochemical and geochronological studies of the volcanic host rocks (the Dahalajunshan Formation) and associated intrusive rocks, particularly the enrichment of large-ion lithophile elements and depletion of high field strength elements, suggest that the Tulasu basin was located in a magmatic-arc setting from Late-Devonian to Early-Carboniferous, associated with the southward subduction of the North Tianshan Ocean beneath the Kazakhstan–Yili plate. Geologic and geochemical characteristics of the AuCu–polymetallic deposits in the Tulasu basin suggest that the mineralization is related to the Late-Devonian to Early-Carboniferous arc magmatism, and is mainly of epithermal nature, including both the adularia–sericite type (Axi, Tawuerbieke and Tabei) and alunite–kaolinite or acid–sulfate type (Jingxi–Yelmend and Tieliekesayi). However, some evidence of porphyry-type mineralization has also been found, including the presence of mineralized porphyry enclaves in volcanic rocks hosting the Tawuerbieke Au prospect, and the development of porphyry-style Cu mineralization overprinted by vein-type mineralization at Kexiaxi. Considering the magmatic-arc setting that is favorable for both epithermal and porphyry types of mineralization, and the development of such mineralization systems in other parts of western Tianshan and the Altaid Belt (e.g., Uzbekistan, Kazakhstan and Kyrgyzstan), we suggest that major porphyry CuAu deposits may have been developed in the Tulasu basin, probably beneath or adjacent to known epithermal Au mineralization.

Chemical and isotopic characteristics of geothermal fluids from Sulphur Springs, Saint Lucia

Sulphur Springs is a vigorous, geothermal field associated with the active Soufrière Volcanic Centre in southern Saint Lucia, Lesser Antilles island arc. The ‘Sulphur Springs Park’ is an important tourist attraction (touted as the ‘world's only drive-through volcano’) with some of the hot pools being developed into recreational pools. Some 200,000 people visit the park each year. Since 2001, the hydrothermal fluids of Sulphur Springs have been sampled as part of an integrated volcanic monitoring programme for the island. Gas and water samples were analysed to characterise the geochemistry of the hydrothermal system, and to assess the equilibrium state and subsurface temperatures of the reservoir. This has also enabled us, for the first time, to establish baseline data for future geochemical monitoring.The gases are of typical arc-type composition, with N2 excess and low He and Ar content. The dry gas composition is dominated by CO2 (ranging from 601–993mmol/mol), with deeper magmatic sourced H2S-rich vapour undergoing boiling and redox changes in the geothermal reservoir to emerge with a hydrothermal signature in the fumarolic gases. Fluid contributions from magmatic degassing are also evident, mainly from the moderate to high contents of HCl and deeply-sourced H2S gas, respectively. Sulphur Springs hydrothermal waters have acid-sulphate type compositions (SO4=78–4008mg/L; pH=3–7), and are of primarily meteoric origin which have been affected by evaporation processes based on the enrichment in both δ18O and δD (δ18O=−1 to 15‰ and δD=−9 to 14‰ respectively) in relation to the global meteoric water line (GMWL). These waters are steam-heated water typically formed by absorption of H2S-rich gases in the near surface oxygenated groundwaters. Reservoir temperatures calculated from the evaluation of gas equilibria in the CO2–CH4–H2 system reveal higher temperatures (190 to 300°C) than those derived from quartz geothermometry (95 to 169°C), which appeared to be affected by dilution with meteoric waters. Generally, no significant variations in fluid geochemistry of the hydrothermal system were observed between 2001 and 2006, and we propose that there were no changes in the state of volcanic activity during this period.

Deep Sea Mining of Submarine Hydrothermal Deposits and its Possible Environmental Impact in Manus Basin, Papua New Guinea

The Manus back-arc basin host three distinct well known submarine hydrothermal deposits of Vienna Wood, Pacmanus and Onsen sites. The Vienna Wood site is a typical Cu-Zn type of mineralization consisting predominantly of pyrite, marcasite, sphalerite, wurtzite and chalcopyrite. The Pacmanus site is a polymetallic type of mineral deposit consisting of sphalerite, chalcopyrite, bornite, wurtzite, pyrite, marcasite, enargite, tennantite, galena, Pb-As-Sulphosalt, gold, covellite, digenite and chalcocite. The Onsen site is the first deep sea acid sulfate type of mineralisationconsisting ofenargite, covellite, chalcopyrite, pyrite and marcasite.The Papua New Guinea (PNG) Government has granted exploration license to Nautilus Mineral Cooperation to explore for submarin e hydrothermal deposit in the Manus Basin. It has done extensive exploration around the existing hydrothermal depos its of Vienna Wood, Pacmanus and Onsen site. This has resulted in the discoveries of well over twenty hydrothermal deposits (Solwara 1 to Solwara 20). Nautilus Minerals has done resource drilling on Solwara 1 and Solwara 12 deposit due to its polymetallic type of mineralization and its geochemicalsimilarities to the Pacmanus site. From resources drilling, Nautilus Minerals reported an indicated and inferred mineral resource of 1030 kt and 1540 kt respectively for the Solwara 1 project at 2.6% Cu equivalent cut off grade. The PNG government has granted mining lease (ML154) to Nautilus Minerals to mine the Solwara 1 deposit in January 2012. If mining activity commences at the Solwara 1 site then Nautilus needs to address possible environmental impacts of water usage and discharge, water quality, sedimentation and dewatering and preservation of hydrothermal vent communities.

Origin of the Matauri Bay halloysite deposit, Northland, New Zealand

At the Matauri Bay halloysite deposit, economically valuable halloysite-rich clays are hosted by a sanidine rhyolite dome (Ar–Ar dated at 10.1 ± 0.03 Ma). The rhyolite dome intrudes an older basalt and is overlain by alluvial sediments and a younger basalt (4.0 ± 0.7 Ma). A blanket-like, halloysite-rich zone is restricted to depths of 10–30 m from the present day erosion surface. Primary sanidine and plagioclase phenocrysts in rhyolite are completely leached out in the halloysite-rich zone but are only partially leached out at greater depth. Halloysite was formed by hydrolysis and cation leaching of sanidine and plagioclase phenocrysts and groundmass glass in the rhyolite, resulting in loss of K, Ca, Na and Si and enrichment in OH (LOI 6–10%) and Al2O3 (20–30%) relative to least-altered rhyolite with 1.8% LOI and 14.5% Al2O3. Oxygen and hydrogen isotope data indicate the halloysite is supergene rather than hydrothermal in origin, which is consistent with the absence of pyrite, alunite and other acid-sulphate type hydrothermal minerals, and with the blanket-like alteration profile. The dominance of halloysite over kaolinite was favoured by water-saturated weathering conditions during the late Miocene-Pliocene subtropical weathering regime in Northland.

Secondary quartzites and their relation to gold mineralization at the Svetloe deposit, Ul’ya Trough, Okhotsk-Chukotka volcanic belt

Hydrothermally altered rocks and their relation to gold mineralization at the Svetloe deposit in the Ul’ya Trough, western sector of the Okhotsk-Chukotka volcanic belt, are studied. The rock composition and style of mineralization are typical of acid-sulfate type deposits. The hydrothermally altered rocks of the deposit are medium-temperature secondary quartzites with developed alunite facies. The upper structural level in the massif of secondary quartzites is made up of a sheetlike body 30 km2 in area and up to 300 m thick with gentle (5–10°) periclinal bedding relative to the arcuate axis of the volcanic range. Below the sheet, there are a number of local steep mostly carinate zones and small (a few hundreds of square meters) multilayered trough-shaped structures, the foot of which is located 100–150 m under the secondary quartzite sheet. All structures of the lower level are restricted to the volcanic range pericline, marked by elevated thicknesses of monoquartzites, and have a gradual transition to the sheetlike part of the massif. The massif of secondary quartzites shows symmetrical zoning. The central zone of the sheetlike body is composed of alunite quartzites framed by dickite varieties. Down the section, the latter grade into hydromica and hydromica-montmorillonite argillic rocks. Monoquartzites form axial zones in the structures of the lower level. In the blanketlike part of the deposit, monoquartzites occur as rare thin lenses and interlayers spatially related to local structures of the lower level. Gold mineralization at the deposit associates with porous monoquartzites. Gold precipitated after quartzite formation during infilling of pores and cavities with colloform silica with barite, and hypogene jarosite.

Clay alteration of volcaniclastic material in a submarine geothermal system, Bay of Plenty, New Zealand

The Calypso Hydrothermal Vent Field (CHVF) is located along an offshore extension of the Taupo Volcanic Zone (TVZ), an area of abundant volcanism and geothermal activity on the North Island of New Zealand. The field occurs within a northeast-trending submarine depression on the continental shelf approximately 10–15 km southwest of the White Island volcano in the Bay of Plenty. The graben has been partially filled by tephra from regional subaerial volcanic eruptions, and active hydrothermal venting occurs at several locations along its length. The vents occur at water depths of 160 to 190 m and have temperatures up to 201 °C. Recovered samples from the vent field include variably cemented and veined volcaniclastic sediments containing an assemblage of clay minerals, amorphous silica, barite, As–Sb–Hg sulfides, and abundant native sulfur. The volcanic glass has been altered primarily to montmorillonite and mixed-layer illite–montmorillonite; illite, and possibly minor talc and mixed-layer chlorite–smectite or chlorite–vermiculite are also present. A hydrothermal versus diagenetic origin for the smectite is indicated by the presence of both illite and mixed-layer clays and by the correlation between the abundance of clay minerals and the abundance of native sulfur in the samples. The mineralization and alteration of the volcanic host rocks are similar to that observed in near-neutral pH geothermal systems on land in the TVZ (e.g., Broadlands–Ohaaki). However, the clay minerals in the CHVF have a higher concentration of Mg in the dioctahedral layer and a higher interlayer Na content than clay minerals from Broadlands–Ohaaki, reflecting the higher concentrations of Mg and Na in seawater compared to meteoric water. Minerals formed at very low pH (e.g., kaolinite and alunite), typical of steam-heated acid-sulfate type alteration in the TVZ geothermal environment, were not found. Mixing with seawater likely prevented the formation of such low-pH mineral assemblages. The occurrence of illite and mixed-layer illite–smectite close to the seafloor in the CHVF, rather than at depth as in the Broadlands system, is interpreted to reflect the higher pressures associated with submarine venting. This allows hotter fluids to be discharged before they boil, and thus minerals that are encountered mainly at depth in subaerial geothermal systems can form close to the seafloor.

Sulfur geochemistry of hydrothermal waters in Yellowstone National Park: IV Acid–sulfate waters

Abstract Many waters sampled in Yellowstone National Park, both high-temperature (30–94 °C) and low-temperature (0–30 °C), are acid–sulfate type with pH values of 1–5. Sulfuric acid is the dominant component, especially as pH values decrease below 3, and it forms from the oxidation of elemental S whose origin is H 2 S in hot gases derived from boiling of hydrothermal waters at depth. Four determinations of pH were obtained: (1) field pH at field temperature, (2) laboratory pH at laboratory temperature, (3) pH based on acidity titration, and (4) pH based on charge imbalance (at both laboratory and field temperatures). Laboratory pH, charge imbalance pH (at laboratory temperature), and acidity pH were in close agreement for pH ±10%, a selection process was used to compare acidity, laboratory, and charge balance pH to arrive at the best estimate. Differences between laboratory and field pH can be explained based on Fe oxidation, H 2 S or S 2 O 3 oxidation, CO 2 degassing, and the temperature-dependence of p K 2 for H 2 SO 4 . Charge imbalances are shown to be dependent on a speciation model for pH values 4 concentrations, in the thousands of mg/L, result from evaporative concentration at elevated temperatures as shown by the consistently high δ 18 O values (−10‰ to −3‰) and a δD vs. δ 18 O slope of 3, reflecting kinetic fractionation. Low SO 4 concentrations ( 350 mg/L Cl) decrease as the Cl − concentration increases from boiling which appears inconsistent with the hypothesis of H 2 S oxidation as a source of hydrothermal SO 4 . This trend is consistent with the alternate hypothesis of anhydrite solubility equilibrium. Acid–sulfate water analyses are occasionally high in As, Hg, and NH 3 concentrations but in contrast to acid mine waters they are low to below detection in Cu, Zn, Cd, and Pb concentrations. Even concentrations of SO 4 , Fe, and Al are much lower in thermal waters than acid mine waters of the same pH. This difference in water chemistry may explain why certain species of fly larvae live comfortably in Yellowstone’s acid waters but have not been observed in acid rock drainage of the same pH.

Subvolcanic hydrothermal systems: Implications from hydrothermal minerals in hydrovolcanic ash

Hydrothermal minerals, including silica, 7 Å-kaolin minerals, pyrophyllite, di-octahedral smectite, and alunite in ash of phreatic/phreatomagmatic eruptions from eight volcanoes in Northeastern Japan were derived from subvolcanic hydrothermal systems. Comparison with internal structures of some extinct volcanoes indicates that hydrovolcanic ash was derived from cores of stratocones at depths of 250–1500 m or greater. The hydrothermal mineral assemblages are similar to those of acid–sulfate type alteration around hydrothermal ore deposit districts. They represent hydrothermal temperatures up to 340 °C. Relative abundance of Ca–K–Na alunite is not correlated with other acid–sulfate minerals because its precipitation reflects only fluid composition, whereas hydrous aluminosilicate and silica minerals reflect base-ion leaching by acidic fluids. Temporal variations in composition and abundances of mineral assemblages at some volcanoes imply the evolution of acid–sulfate alteration zones.

Kaolin Occurrences in the Erenler Dagi Volcanics, Southwest Konya Province, Turkey

Mainly calc-alkaline, andesitic, and dacitic volcanics from different late Miocene-Pliocene eruption centers crop out WSW of Konya, and locally are interbedded with lacustrine sediments. Hydrothermal alteration within these rocks is widespread. In addition to kaolinite, other major alteration products include halloysite, alunite, cristobalite, quartz, illite, montmorillonite, and zeolitegroup minerals. Based on the cristobalite-quartz relationship, the kaolinization temperature is estimated as ∼100°C. The samples were mineralogically and chemically examined using XRD, SEM-EDS, IR, DTA-TG, and XRF. The crystallinity of the kaolinite is moderate, and shows structural disorder. Both the kaolinite and halloysite are almost stoichometric. Kaolinization generally led to Al2O3 increases and release of alkalies, alkaline earths, most of the Fe2O3, and SiO2. SiO2 and Al2O3 contents are low, and LOI is very high for halloysite deposits relative to kaolin occurrences. The kaolinite-alunite assemblages indicate that pH of the altering solutions initially was ∼4. SEM investigation demonstrates that kaolinite has booklet texture, whereas halloysite is acicular to needleshaped. The chemical, mineralogic, and firing properties of the kaolin deposits are appropriate for use as refractory raw material. The Erenler Dagi kaolin deposits are excellent examples of the acid-sulfate type of hydrothermal alteration. The findings of the study may be useful in exploration for similar hydrothermal mineral occurrences worldwide.

Acid‐sulphate Type Alteration and Mineralization in the Desmos Caldera, Manus Back‐arc Basin, Papua New Guinea

Abstract: The Onsen acid‐sulphate type of mineralization is located in the Desmos caldera, Manus back‐arc basin. Hydrothermal precipitates, fresh and altered basaltic andesite collected from the Desmos caldera were studied to determine mineralization and mobility of elements under seawater dominated condition of hydrothermal alteration.The mineralization is characterized by three stages of advanced argillic alteration. Alteration stage I is characterized by coarse subhedral pyrophyllite with disseminated anhedral pyrite and enargite which were formed in the temperature range of 260–340°C. Alteration stage II which overprinted alteration stage I was formed in the temperature range of 270–310°C and is characterized by euhedral pyrite, quartz, natroalunite, cristobalite and mixed layer minerals of smectite and mica with 14–15 Å XRD peak. Alteration stage III is characterized by amorphous silica, native sulphur, covellite, marcasite and euhedral pyrite, which has overprinted alteration stages I and II.Relative to the fresh basaltic andesite samples, the rims and cores of the partly altered basaltic andesite samples have very low major, minor and rare earth elements content except for SiO2 which is much higher (58–78 wt%) than SiO2 content of the fresh basaltic andesite (55 wt%). REE patterns of the partly altered basaltic andesite specimens are variably depleted in LREE and have pronounced negative Eu anomalies. Normalization of major, minor and REE content of the partly altered basaltic andesites to the fresh basaltic andesite indicates that all the elements except for SiO2 in the partly altered basaltic andesite are strongly lost (e.g. Al2O3 = ‐8.3 to ‐10.9 g/100cm3, Ba = ‐2.2 to ‐5.6 mg/100cm3, La = ‐130 to ‐200 μg/100cm3) during the alteration process. Abnormal depletion of MgO, total Fe as Fe2O3, LREE especially Eu and enrichment of SiO2 in the altered basaltic andesites from the Desmos caldera seafloor is caused by interaction of hot acidic hydrothermal fluid, which originates from a mixing of magmatic fluid and seawater.

Evolution of Sb mineralisation in modern fold belts: a comparison of the Sb mineralisation in the Central Andes (Bolivia) and the Western Carpathians (Slovakia)

In the Central Andes (Bolivia) and the Western Carpathians (Slovakia) Sb-(Au) deposits are of wide-spread occurrence. They may be subdivided into two principal types: (I) shear zone-hosted and (II) stockwork-like Sb deposits. Type I Sb deposits are widespread in fine-grained metasedimentary, granitic and gneissic rocks. Type II is only found in volcanic rocks and may be further subdivided into acid sulphate-type (IIa) and low sulphidation-type (IIb). This more subtle classification is based upon the presence or absence of sulphate and K feldspar and applied in the same way as for epithermal Au deposits elsewhere. Type III is a composite vein type transitional between types I and II Sb deposits. Mesothermal deposits (type I) were emplaced syntectonically and synmetamorphically under low grade to very low grade stage metamorphic conditions. The mineralising fluids are likely to have been derived from crustal sources through devolatalisation. Epithermal types (IIa) and (IIb) are related in time and space with the formation of acidic to intermediate (sub)volcanic rocks of Miocene age. To distinguish the various types of Sb mineralisation, Bi, Ag, As and Hg have proven most diagnostic. These elements are anomalously enriched in the volcanic-hosted types IIa and IIb, whereas type I mineralisation are poor in Bi, Ag and As. The element contents of these trace elements in type III deposits vary according to the position of the host mineralisation relative to the Tertiary igneous rocks. Hg tends to be enriched in type II mineralisations. Even so there are also some Sb mineralisations of type I abundant in Hg, possibly due to tetrahedrite intergrown with stibnite. In contrast to porphyry copper deposits, Sb deposits are distal relative to the subduction zone. They are confined to sections of the fold belt where the continental crust is thick and was subject to strong horizontal displacements. The ratio of horizontal to vertical crustal movements during the structural evolution of the fold belt and the resultant skewness of the geothermal gradient played a decisive role for the type of volcanic-hosted Sb deposits (types IIa and IIb) to develop and to what extent composite stibnite deposits (type III) evolved.

Physico-chemical analysis of mineral parageneses of the advanced argillic rock alteration at Pod Polomon in porphiry copper systems, Javorie, Slovak Republic

Physico-chemical analysis of the mineral parageneses of argillic type of altered rocks in Pod Polomom porphyry copper system of Javorie, Slovackia. In the zone of advanced argillizaton of the rocks occurring in the shallow parts of the porphyry copper system of Javorie, the Pod Polomom quarry, the following associations are presented: quartz + pyrophyllite, quartz + pyrophyllite + diaspore, quartz + pyrophyllite + topaz, quartz + pyrophyllite + diaspor + topaz, quartz + topaz, quartz + zunyite. A physico-chemical analysis of the mineral parageneses has been applied in order to distinguish the equilibrium mineral association (mineral parageneses), that appear as important for the genetic classifications. The prognostic paragenetic diagram obtained is the basis for analysis of physico-chemical formation conditions of mineral parageneses rich in aluminium non-sulphate mineral phases. Beside the acid-sulphate type of alteration the pyrophylite-diaspore and fluoride (topaz-zunyite) types of alteration are assigned to the advanced argillization. The facial analysis allows to identify the pyrophyllite-diaspore, topaz and zunyite facies of the secondary quartzite formation that correspond to those types of alteration. This investigation proposes unifying features of the two commonly accepted genetic classifications according to types of alterations and to formations respectively.

The application of imaging spectrometry data to mapping alteration zones associated with gold mineralization in southern Spain

Abstract The gold mineralization at the Rodalquilar mine in southern Spain is of the acid-sulphate type. We have assessed the ability of AVIRIS imaging spectrometer data to detect the hydrothermal alteration mineralogy mapped using traditional ground-based techniques at Rodalquilar. Four methods of retrieving apparent surface reflectance have been evaluated, the empirical line method and three methods of radiative transfer modelling. This study indicates that radiative transfer modelling, using only atmospheric information derived from the imaging spectrometry data, can satisfactorily correct the atmospheric effects involved in retrieving apparent surface reflectance. The alteration at Rodalquilar is characterized by propylitic (vermiculite), illitic, kaolinitic (pyrophyllitic), alunitic and silicic zones with an increasing degree of alteration towards the formative hydrothermal cells in whose fossil cores the gold mineralization is found. However, several factors act against the usefulness of the AVIRIS data for mapping these mineral zones: the mine site is heavily disturbed with exposed workings, often of high albedo altered rocks, whilst unworked areas have partial iron-rich soil and dry vegetation cover; the alteration itself is highly discontinuous at the scale of 10 m and the shortwave infrared (SWIR) data where much of the diagnostic information for these hydrothermal minerals lies is very noisy. Nevertheless it has proved possible to map successfully, at the individual pixel level, the zones of gold-bearing alunitic alteration using the joint presence of alunite absorption features at 1480 and 1760 nm. The data from the 2000-2400 nm spectral range allow the areas with general absorption features centred around 2200 nm to be mapped but zonation based on individual minerals identification is not possible.

Apparent ages of hydrothermal alteration zones in the North Arm Volcanics, southeast Queensland

The North Arm Volcanics in southeast Queensland contain two large zones of hydrothermal alteration imposed on rhyolitic and dacitic rocks. At the North Arm prospect, alteration encloses epithermal vein‐ and breccia‐hosted Ag‐Au mineralization and has characteristics of the adularia‐sericite type. The other zone, at Mt Ninderry, is of acid sulphate type. Both zones are considered to be temporally related on geological, alteration and stable isotopic criteria. A K‐Ar age of 217 ±2 Ma for an alunite‐bearing whole‐rock at Mt Ninderry is consistent with the Late Triassic age of the felsic phase of the North Arm Volcanics, as determined by published radiometric and palaeobotanical methods. However, at North Arm prospect, K‐Ar and Rb‐Sr data for sericite (‐K feldspar)‐altered whole‐rocks yield apparent ages in the range 182–186 Ma (Middle Jurassic) and for separated sericite, ages in the range 152–166 Ma (Late Jurassic). The probability of hydrothermal episodes occurring within the Middle Jurassic, and within th...

Geothermal prospecting in the Semporna Peninsula with emphasis on the Tawau area

Thermal manifestations in the Semporna Peninsula include hot springs, seepages, mud pools and old steaming ground. Mapping of these thermal features showed that they are structurally controlled. The chemistry of the thermal waters indicate the presence of two types of waters - near neutral sodium chloride and sulphate waters. Thermal waters from the Apas Kiri area are near-neutral sodium chloride waters and the C11B and C11F ratios suggest they have a common source of geothermal fluid. The thermal water from upper Tawau is acid sulphate type and its chemistry suggests it is steam-heated water or ground water mixed with gas (H2S). The chemistry of thermal waters from Balung and Sungai Jepun areas suggests they are acid sulphate waters which may have come from a far away source and come into contact with and neutralised by cold ground water. The upper Tawau and Balung springs may indicate the perimeter of a field centered on the Maria Volcanic Complex. The Apas Kiri area is underlain mainly by Quaternary dacitic lava, tuff and agglomerate. The surface thermal manifestations cover an area of 3 km'. The volcanic rocks are calcitised, chloritised, argillised and pyritised. Around the thermal features, the rocks are strongly argillised and calcitised. Several characteristics of the Apas Kiri thermal waters e.g. chloride contents, ClIB ratio and geothermometer suggest high subsurface temperature. The ClIB ratio also suggests the reservoir rocks are andesitic. Total heat loss from the Apas Kiri 2, Apas 5 and Sungai Jepun areas have been tentatively estimated as 28.65, 0.75 and 15.05 MW-Thermal respectively.