NaCl Eq Research Articles

The Formation Conditions and Sources of Ore-Forming Fluids of the Nikolaevskoe Gold Deposit (South Urals)

Abstract —We studied fluid inclusions, trace elements, and oxygen, carbon, and sulfur isotope ratios in minerals from stockwork sulfide–carbonate–quartz ores of the Nikolaevskoe gold deposit confined to volcanic island arc porphyry intrusions. The study shows that fluid inclusions in quartz were homogenized at 260–200 ºС and those in later formed calcite, at 227–205 ºС. The fluids contain aqueous K– Mg–Na chloride solutions with salinity of 4.1–9.6 wt.% NaCl eq. Raman spectroscopy revealed СO2 (29–34 mol.%), CH4 (40–55 mol.%), and N2 (8–30 mol.%) in the fluids. According to LA-ICP-MS data, quartz has low contents of Al (11.7–102 ppm) and Ti (0.05–0.64 ppm), which indicates its deposition from weakly acid low-alumina fluids at <350 ºС. The REE patterns of calcite show accumulation of heavy lanthanides (LaN/YbN = 0.2–0.9), evident of high fluid alkalinity, and negative Ce (0.39–0.82) and positive Eu (1.99–5.25) anomalies. The negative Ce anomalies are due to meteoric water in the fluid and the fluid interaction with limestones. The positive Eu anomalies reflect the high-temperature (>250 ºC) environment that existed before the calcite crystallization. The Y/Ho ratio in calcite (28.7–54.1) suggests that the fluid has magmatic components and components extracted from limestones and contains seawater. The δ18OH2O values (3.6–5.6‰) of the fluid testify to the participation of magmatic and meteoric waters in the ore formation. The δ13CCO2 values (–4.1 to 1.4‰) point to carbon of magmatic nature and carbon extracted from limestones. The heavy sulfur isotope composition of pyrite (6.75 to 9.87‰) and arsenopyrite (8.7‰) might be due to sulfur supply from the host rocks or to the participation of [SO4]2- of seawater in the ore-forming process. According to the results obtained, the Nikolaevskoe gold deposit is an island arc (Au ± Cu)–quartz–sulfide deposit transitional between porphyry and epithermal types.

Fossil travertine system and its palaeofluid provenance, migration and evolution through time: Example from the geothermal area of Acquasanta Terme (Central Italy)

The geothermal area of Acquasanta Terme has often been studied for its active and fossil travertine deposits to elucidate fluid origin, geodynamic and hydrological setting. Even though present-day thermal springs are usually used to obtain most information, the three travertine terraces bordering the Tronto river contain a plethora of information. A combination of elemental and isotope analyses (δ18O, δ13C and 87Sr/86Sr-ratio), fluid inclusion microthermometry and UTh dating is used to verify the hydrogeology and its timing. These analyses point out two fluid reservoirs with distinctly different fluids, one with low salinity of 0.7 wt% NaCl eq. and another with 28.5 wt% NaCl eq., which corresponds to the fluid composition of present-day spring fluids. Furthermore, it is demonstrated that geothermal sources were intermittently active in the past 221 ka mainly during uneven-numbered marine isotope stages, which are related to humid, interglacial periods and resulted in three different travertine terraces around 210.5, 126.5, and 36.5 ka. Accordingly, an uplift rate for this area could be estimated at around 1 mm/ka. The fluids were tapped at a depth of approximately 3 km in the tectonized, cataclastic fraction of the Triassic Anidriti di Burano Formation, the Calcare Cavernoso Formation and are originally meteoric based on geochemical evidence of a uniform 87Sr/86Sr-ratio of 0.707914 ± 0.00019 and a δ18Oaragonite value of −11.90 ± 0.34‰, which has been depressed by elevated precipitation temperatures between 22.2 and 50 °C. The characterization and dating of fossil travertine deposits gives valuable data providing insights in long-term fluid flow and orogenic uplift rates, adding valuable information to present-day spring fluid characterization.

Extreme fractionation and magmatic–hydrothermal transition in the formation of the Abu Dabbab rare-metal granite, Eastern Desert, Egypt

The Abu Dabbab rare-metal granite in the Central Eastern Desert of Egypt is a peraluminous alkali-feldspar leucogranite stock with minimummelt composition of albite-rich haplogranite and is characterized by economic resources of columbite group minerals (CGM) and cassiterite. The bulk-rock trace element composition is characterized by very low Sr, Ba, REE+Y, Zr, Ti, Ni, Cr concentrations, elevated Li and F, and very high Sn, Ta and Ga. The non-chondritic, low Y/Ho ratios and extremely low Nb/Ta and Zr/Hf ratios of the Abu Dabbab granite are consistent with highly evolved peraluminous granites. The chondrite-normalized REE patterns with significant tetrad effects (TE1,3 ~ 1.6–2.6) and strongly negative Eu anomalies are indicative of the magmatic to hydrothermal transition. Heterogeneous 147Sm/144Nd (0.20411–0.51923) and 143Nd/144Nd (0.512968–0.514056) values of the bulk-rock reflect a disturbed Sm-Nd isotope system. Nevertheless, the initial εNd values calculated for a wide range of Neoproterozoic ages (500–700 Ma) are consistently positive, suggesting a juvenile source.Laser ablation ICP-MS analyses of the CGM, cassiterite, wolframite and Mn-ilmenite show elevated rare metal concentrations and complex REE tetrad patterns, reflecting fluid-melt interactions. The metasomatic fluids associated with the Abu Dabbab rare-metal granite were primarily low-salinity (<6 wt.% NaCl eq.), high-density (~0.8–0.9 g/cm3), CO2-rich aqueous fluids with up to ~50 mol% CO2 (+CH4). The minimum entrapment conditions of carbonic-aqueous inclusions are calculated as 2–3 kbar and 350–360°C, whereas aqueous inclusions in the granite and crosscutting quartz veins most likely correspond to lower-pressure conditions and fluid phase separation by decompression. The extreme level of fractionation and complex tetrad effects of the bulk-rock and ore minerals coupled with criteria indicating the magmatic-hydrothermal transition are in accord with regional seismic tomography and heat flow data. A much larger, unexposed parental granite system, from which the exposed Abu Dabbab rare-metal tip has fractionated, must be present at depth. The interaction between extreme fractionation and fluid-melt interaction at shallow crustal levels gave rise to economic-grade Ta-Nb-Sn±W mineralization in the granite body and associated quartz veins.

Geological and geochemical constraints on the Farahabad vent-proximal sub-seafloor replacement SEDEX-type deposit, Southern Yazd basin, Iran

Farahabad is a Lower Cretaceous-age sandy dolomite, sandstone and silty limestone hosted zinc-lead deposit in the southern Yazd basin, Iran. This deposit occurs in the lower part of Taft Formation. The Farahabad deposit is a stratiform and stratabound accumulation of hydrothermal sulfides. The mineralized zone at Farahabad is lens shaped and has a relatively flat top. It also ranges greatly in thickness, from a few meters to >30 m. Three styles of ore facies have been differentiated at the deposit. Feeder zone, bedded ore facies, whereas the bulk of ore is contained within sphalerite and galena breccias that record a prolonged and texturally complex history of ore replacement (massive-replacement ore facies). The shape and size of the mineralized body suggest that dolomites replaced with sulfide minerals in a submarine channel. Dolomitization and sulfide mineralization's are the major hydrothermal products in the Farahabad deposit, and they occur in all host rocks, but only in the immediate vicinity of the syn-sedimentary normal fault that served as the main conduit for the mineralizing fluids. Based on microscopic studies, sulfide mineralization in the Farahabad deposit emplaced during two stages: fine-grained sulfide bands (stage I) are intricately interlayered with organic matter-rich beds and thin turbidite beds. They exhibit classic sedimentary textures, such as laminae, cross bedding, graded bedding and bedding, indicative of a synsedimentary origin. Main-stage (stage II) mineralization involved the progressive replacement of preexisting sulfides and the dolomite breccias, initially by replacement of the breccia matrix and ultimately by replacement of clasts.Dolomite minerals from the feeder zone and massive-replacement ore facies have 115–234 °C trapping temperature with salinities ranging from 0.99 to 16.70 eq. wt% NaCl eq. δ34S values of sulfide minerals range from −19.47 to +3.9‰, suggesting that sulfur in the hydrothermal fluids was derived predominantly from reduction of seawater sulfate by bacteriogenic sulfate reduction. The δ13CPDB and δ18OSMOW values of host limestone's and hydrothermal dolomites plot the near marine carbonate rocks field in a plot of δ13CPDB vs. δ18OSMOW diagram. It suggests that CO2 in the hydrothermal fluids was mainly originated from marine carbonate rocks. Abrupt lateral changes in facies and thickness, along with the existence of synsedimentary breccia's and debris flows within the ore sequence, suggest the proximity of synsedimentary faults and tectonic activity contemporaneous with the sedimentation in the Lower Cretaceous, favorable to the formation of deposit. So this deposit formed by combination of sub-seafloor replacement and on the seafloor processes. Characteristics of the Farahabad deposit are compatible with a vent-proximal sub-seafloor replacement SEDEX-type classification.

Cu–Mo Differential Mineralization Mechanism of the Dabate Polymetallic Deposit in Western Tianshan, NW China: Evidence from Geology, Fluid Inclusions, and Oxygen Isotope Systematics

AbstractClassic porphyry Cu–Mo deposits are mostly characterized by close temporal and spatial relationships between Cu and Mo mineralization. The northern Dabate Cu–Mo deposit is a newly discovered porphyry Cu–Mo polymetallic deposit in western Tianshan, northwest China. The Cu mineralization postdates the Mo mineralization and is located in shallower levels in the deposit, which is different from most classic porphyry Cu–Mo deposits. Detailed field investigations, together with microthermometry, laser Raman spectroscopy, and O‐isotope studies of fluid inclusions, were conducted to investigate the origin and evolution of ore‐forming fluids from the main Mo to main Cu stage of mineralization in the deposit. The results show that the ore‐forming fluids of the main Mo stage belonged to an NaCl + H2O system of medium to high temperatures (280–310°C) and low salinities (2–4 wt% NaCl equivalent (eq.)), whereas that of the main Cu stage belonged to an F‐rich NaCl + CO2 + H2O system of medium to high temperatures (230–260°C) and medium to low salinities (4–10 wt% NaCl eq.). The δ18O values of the ore‐forming fluids decrease from 3.7–7.8‰ in the main Mo stage to −7.5 to −2.9‰ in the main Cu stage. These data indicate that the separation of Cu and Mo was closely related to a large‐scale vapor–brine separation of the early ore‐forming fluids, which produced the Mo‐bearing and Cu‐bearing fluids. Subsequently, the relatively reducing (CH4‐rich) Mo‐bearing, ore‐forming fluids, dominantly of magmatic origin, caused mineralization in the rhyolite porphyry due to fluid boiling, whereas the relatively oxidizing (CO2‐rich) Cu‐bearing, ore‐forming fluids mixed with meteoric water and precipitated chalcopyrite within the crushed zone at the contact between rhyolite porphyry and wall rock. We suggest that the separation of Cu and Mo in the deposit may be attributed to differences in the chemical properties of Cu and Mo, large‐scale vapor–brine separation of early ore‐forming fluids, and changes in oxygen fugacity.

Ouansimi copper mineralization (Western Anti-Atlas, Morocco): Paragenetic sequence and circulation of gangue hosted paleofluids.

The Ouansimi copper deposit, located South of the Kerdous inlier in Morocco, is an example of vein-type mineralization hosted in the Adoudou Formation limestone of the Lower Cambrian Taroudant Group. The copper-bearing veins are mainly controlled by Variscan NNW-trending faults and are subdivided here into Eastern, Western, and Central structures. On the basis of mineralogical, metallographic, and fluid inclusion studies, two mineralizing processes are proposed. A primary process is interpreted for the chalcopyrite, digenite, galena, sphalerite, carrollite, and pyrite with quartz and dolomite as gangue minerals. A secondary process is proposed for chalcocite, bornite, covellite, native copper, copper carbonate and oxide. Microthermometric analysis of fluid inclusions was carried out on quartz and dolomite gangues. Primary fluid inclusions trapped in quartz show the existence of fluids with temperatures of 175°C–275 °C and salinities of 10–15 wt % NaCl eq. However, fluid inclusions in dolomite indicate fluids with temperatures of 200°C–250 °C and salinities of 20–25 wt % NaCl equiv. Combining ore mineralogy and fluid inclusion microthermometry, two main hypogene sulphide mineralization stages can be distinguished in the Ouansimi copper deposit. The first Cu–Fe stage, with quartz as a gangue mineral, was related to hydrothermal fluids with moderate temperature and low salinity. The second Cu–Zn–Pb–Co–Ni–Fe stage was associated with dolomite as a gangue mineral and infilled cavities and fractures cutting quartz. This second phase was related to hydrothermal fluids with moderate temperature and high salinity. The tectonic evolution of the Ouansimi deposit was characterized by thrusting of the south limb over the north limb and by dextral and sinistral offsets of the mineralized structures along late-stage ENE-WSW-trending faults.

Genesis of the Jinchanggouliang gold deposit, Chifeng, China: Constraints from fluid inclusions and isotopic geochemistry

The Jinchanggouliang gold deposit which located south of the Hingan-Mongolian Orogenic Belt is a large gold deposit in the Chifeng-Chaoyang region. Field evidence and petrographic observations indicate that the mineralization processes can be divided into three stages: including milky or grey quartz (stage I), quartz-pyrite (stage II), quartz-polymetallic sulfides (stage III). Five types of FIs have been identified in the Jinchanggouliang deposit: (1) solid-bearing inclusions (type 1), liquid-rich inclusions (type 2); vapor-rich inclusions (type 3); pure vapor inclusions (type 4) and CO2–H2O inclusions (type 5). The first stage contains mainly type 2, but also minor type 3 and 4 FIs; the FIs display homogenization temperatures of 317–384 °C and salinities of 4.0–12.5 wt% NaCl eq. The stage II contains all types of FIs (mainly type 2, less abundant type 3 and 5, rarely type 1 and 4) which show homogenization temperatures of 288–382 °C and salinities of 1.6–41.4 wt% NaCl eq. The types of FIs in stage III are the same as stage II; These FIs yield the lowest homogenization temperatures of 245–363 °C and salinities of 1.1–36.8 wt% NaCl eq. The ore-forming fluids are characterized by moderate-high temperature and great fluctuating salinity magmatic hydrothermal fluids. The type 2 and 3 FIs commonly coexist with simultaneously trapped type 5 FIs, and the type 2 and 3 FIs have similar homogenization temperatures but contrasting homogenization modes (to the liquid and vapor, respectively) in the main mineralization stages which suggests fluid boiling occurred in these two stages. Combined with the previous H-O isotopic data it can be concluded that the ore-forming fluids are of granitic magmatic origin. The S-Pb isotopes indicate that the ore materials were mainly derived from deep magma. Petrographic observations and microthermometric analysis indicating that fluid boiling was the main mineral precipitation mechanism, and fluid boiling mainly occurred in the temperature range from 290 °C to 370 °C. In general, from the view of fluid inclusions and isotopes geochemistry, the Jinchanggouliang gold deposit is most probably a magmatic hydrothermal deposit.

The Barika gold-bearing Kuroko-type volcanogenic massive sulfide (VMS) deposit, Sanandaj-Sirjan zone, Iran

The Barika deposit is the first documented auriferous Kuroko-type volcanogenic massive sulfide (VMS) deposit in Iran. It is hosted in meta-andesites of the Sanandaj-Sirjan metamorphic Zone (SSZ). The mineralization and host rocks have been metamorphosed to lower greenschist facies. The deposit has Au and Ag grades in the stratiform lens averaging 3.5 and 175 g/t, respectively, and contains 2.3 tonnes of Au and 143 tonnes of Ag. The base metal (Pb + Zn + Cu) content of the deposit is low (<1 wt%). The stratiform part of the Barika deposit is approximately 150 m long and up to 20 m thick, and consists of massive to semi-massive sulfides, some of which are banded, which are overlain by barite and siliceous exhalites. The >200 m long and up to 500 m wide stringer zone immediately stratigraphically underlies the stratiform mineralization. Veins within the stringer zone are composed of quartz, pyrite, galena, sphalerite, tetrahedrite-tennantite, and rare chalcopyrite. Stratiform mineralization is composed of pyrite, sphalerite, galena, stibnite, tetrahedrite-tennantite, several Ag-(As-Sb-Pb) sulfosalt minerals (guettardite, ferdowsiite, barikaite, stephanite, pyrargyrite, trechmannite, miargyrite, As-rich andorite, As-rich geocronite, Sb-rich seligmanite and smithite), realgar, and electrum.Based on mineral assemblages and textures, four mineralization stages are recognized. During stage 1, pyrite, sphalerite, galena, tetrahedrite-tennantite, and stibnite were deposited during synvolcanic hydrothermal activity. During stages 2 and 3, post-mineralization deformation and shearing contemporaneous with regional metamorphism modified most of the primary textures in the stratiform mineralization. Stage 2 mineralization represents Stage 1 mineralization that was remobilized during regional metamorphism, and this mineralization is characterized by gold as submicroscopic inclusions or as “invisible” gold locked in pyrite, as well as electrum in the barite mineralization. Regional metamorphism and deformation (D1) caused recrystallization of primary mineralization (mainly pyrite) and migration of submicroscopic gold via solution-precipitation creep to the grain boundaries to form microscopic electrum. Stage 3 mineralization is attendant with D2 movement along the Barika shear zone that controlled the overall geometry of the deposit and resulted in the development of ductile-brittle deformation textures and the formation of several Ag(As-Sb-Pb)-rich sulfosalt minerals and electrum. Most of the electrum grains occur together with sulfosalt minerals that fill open spaces formed during shearing. Stage 4 mineralization is marked by the formation of white, barren quartz veins and high-angle normal faults that were developed during D3 extension-related uplift.Primary two-phase fluid inclusions in quartz of the stringer zone and barite from the stratiform mineralization homogenize between 132° and 283 °C (average ~ 200 °C). Salinities of the primary fluid inclusions range from 1.4 to 9.6 wt% NaCl eq. The sulfur isotope compositions of sulfide minerals from stratiform and stockwork mineralization in the Barika deposit range from δ34S −0.8 to +5.6‰. This relatively narrow range suggests that the sulfur in the sulfide mineralization was derived from the leaching of igneous sulfur from the underlying andesitic rocks, similar to most Japanese Kuroko VMS deposits. Temperatures of formation for Barika sulfides estimated based on sulfur isotope values for coexisting galena-sphalerite (Δ = 2–4.8‰) and galena-pyrite (Δ = −3.3 to −5.4‰) pairs range from 146 to 293 °C, and these are consistent with fluid inclusion homogenization temperatures. The primary mineralizing fluids have a calculated δ18O value of between +4.3and +6.3‰, based on the δ18O compositions of quartz from the stringer zone and assuming a temperature of 200 °C and that isotopic equilibrium was attained.

Geological characteristics, fluid inclusions and H-O-C-S isotopes of the Zaopa Ag-Mo prospect in the Suizao area, Hubei Province: Implications for ore genesis

The Zaopa Ag-Mo prospect is located in the Tongbai-Dabie orogenic belt in central China. The orebodies occur as quartz veins and are controlled by secondary faults of the Wushan fault zone in the Suizao area, and hosted by the Zhoulou granite. We document three hydrothermal stages, characterized by albite-quartz-sulfide veins (stage I), quartz-sulfide (stage II) and quartz-fluorite assemblages (stage III), respectively. Silver is mainly found in hessite and galena. There are three types of fluid inclusions in quartz and fluorite including: (1) liquid-rich aqueous fluid inclusions (L + V); (2) aqueous-carbonic fluid inclusions (L + V + CO2); (3) pure carbonic fluid inclusions (pure CO2). Laser Raman spectroscopic analyses indicate the existence of carbon dioxide in the fluid inclusions. The fluid system of the Zaopa Ag-Mo prospect is composed of CO2-NaCl-H2O. The homogenization temperatures of the three stages are 380 to 495 °C, 337 to 404 °C and 246 to 336 °C, respectively. The salinities of the three stages are 11.1–17.5 wt% NaCl eq., 6.7–12.7 wt% NaCl eq. and 1.6–9.9 wt% NaCl eq., respectively. The stage I sulfides (molybdenite, chalcopyrite, pyrite) show a δ34S value around 0‰ (−3.1 to +1.0‰), indicating a magmatic origin. The stage II sulfides (galena, sphalerite, pyrite) also show a δ34S value around 0‰ (−5.7 to +1.6‰), again indicating a magmatic origin. The C-H-O isotope data shows that the fluids of the early stage were derived from a magmatic source, but the fluids of the late stage mixed with meteoric waters. By comparing the characteristics of the Mo deposits in China and those from other countries, we conclude that the Zaopa Ag-Mo prospect is a structurally-controlled magmatic-hydrothermal vein type deposit.

Sequential evolution of Sn–Zn–In mineralization at the skarn-hosted Hämmerlein deposit, Erzgebirge, Germany, from fluid inclusions in ore and gangue minerals

Skarn-hosted deposits can be important high-grade resources for a variety of metals, but Sn skarns are still of subordinate importance for global mining because of their complex mineralogy and evolution. As part of recent exploration efforts, the economic potential of the Sn–Zn–In mineralization at the Hammerlein skarn-hosted deposit is currently being re-evaluated. The temporal and spatial evolution of the ore-forming hydrothermal system is still debated. We analyzed fluid inclusion assemblages (FIA) in ore and gangue minerals using conventional and infrared microthermometry and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We further estimated alteration temperatures with chlorite thermometry and compared the fluid inclusion (FI) record at Hammerlein with a mineralized greisen sample of the nearby Eibenstock granite. Cassiterite in skarn forms the major mineralization at Hammerlein during stage I and hosts FIs showing homogenization temperatures of up to 500 °C and salinities between 30 and 47 wt% NaCl eq. Cassiterite from schists and the additional greisen sample from the Eibenstock granite of the later stage II show lower homogenization temperatures (350–400 °C) and considerably lower salinities varying from 1.9 to 6 wt% NaCl eq. Despite the different homogenization temperatures and salinities, the chemical compositions of FIs hosted in both generations of cassiterite show that both (cassiterite in skarn and in schist and greisen) are similar, which points to a common source. The gangue minerals mainly contain low-temperature FIA (max. 330 °C and 2–9 wt% NaCl eq.) and are interpreted to form during further cooling of the system in stage III. Intergrown chlorite has compositions indicating similar temperatures of around 260 °C and is thus also related to stage III. FIA in sphalerite homogenize around 200 °C with salinities between 2 and 6.7 wt% NaCl eq. and show decreasing trace element contents despite having the same salinity range as the gangue minerals, indicating dilution of the ore-fluid during stage IV as a possible precipitation mechanism. Stage I inclusions are solely hosted in cassiterite from skarn, which shows the importance of fluid inclusion analyses in ore minerals, and record remarkable high mineralization temperatures, exceeding the typically temperature range reported in other studies by at least 100 °C. Our results suggest that this main ore stage is related to the early expulsion of a high-salinity brine phase from an underlying magmatic intrusion at depths greater than 3 km, which likely is a relatively short-lived event within the evolution of the hydrothermal system.

Karakteristik Fluida Hidrotermal Endapan Emas Orogenik di Pegunungan Rumbia, Kabupaten Bombana, Provinsi Sulawesi Tenggara

Recently, gold exploration activities are not only focused along volcanic-magmatic belt but also starting to shift along metamorphicand sedimentary terrains. The purpose of this study is to analyses the characteristics hydrothermal fluids gold deposits t in the Rumbia Mountains, Bombana Regency, Southeast Sulawesi. There are three generations of veins identified including 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. Temperature of homogenization (Th) and salinity at Rumbia Mountain of the first vein vary from 220 to 355.30oC and 6.74 to 10.11 wt. % NaCl eq., respectively. The second generation vein was originated at Th of 157 to 255.50oC and salinity of 3.39 to 6.88 wt.%NaCl eq., whereas the third generation vein formed at lowest Th varying from 104.40 to 265.90oC and less saline fluid at salinity range between 0.18 and 6.30 wt.% NaCl eq. The result of temperature formation value correlation to the depth of the formation of orogenic gold deposits in Rumbia Mountain is indicated to form on sub-greenschist to greenschist facies at depth of about 4-8 kilometers and formation temperature between 104.40 - 355.30oC at zone epizonal and mesozonal. Based on characteristics fluids inclusion discussed above, the primary metamorphic-hosted gold mineralization type at Rumbia Mountain tends to meet the criteria of orogenic gold type. Keyword : fluid iclusion, quartz veins, Rumbia mountain, orogenic gold deposits.

Karakteristik Fluida Hidrotermal Endapan Emas Orogenik di Pegunungan Rumbia, Kabupaten Bombana, Provinsi Sulawesi Tenggara

Recently, gold exploration activities are not only focused along volcanic-magmatic belt but also starting to shift along metamorphicand sedimentary terrains. The purpose of this study is to analyses the characteristics hydrothermal fluids gold deposits t in the Rumbia Mountains, Bombana Regency, Southeast Sulawesi. There are three generations of veins identified including 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. Temperature of homogenization (Th) and salinity at Rumbia Mountain of the first vein vary from 220 to 355.30oC and 6.74 to 10.11 wt. % NaCl eq., respectively. The second generation vein was originated at Th of 157 to 255.50oC and salinity of 3.39 to 6.88 wt.%NaCl eq., whereas the third generation vein formed at lowest Th varying from 104.40 to 265.90oC and less saline fluid at salinity range between 0.18 and 6.30 wt.% NaCl eq. The result of temperature formation value correlation to the depth of the formation of orogenic gold deposits in Rumbia Mountain is indicated to form on sub-greenschist to greenschist facies at depth of about 4-8 kilometers and formation temperature between 104.40 - 355.30oC at zone epizonal and mesozonal. Based on characteristics fluids inclusion discussed above, the primary metamorphic-hosted gold mineralization type at Rumbia Mountain tends to meet the criteria of orogenic gold type. Keyword : fluid iclusion, quartz veins, Rumbia mountain, orogenic gold deposits.

Karakteristik Fluida Hidrotermal Endapan Emas Orogenik di Pegunungan Rumbia, Kabupaten Bombana, Provinsi Sulawesi Tenggara

Recently, gold exploration activities are not only focused along volcanic-magmatic belt but also starting to shift along metamorphicand sedimentary terrains. The purpose of this study is to analyses the characteristics hydrothermal fluids gold deposits t in the Rumbia Mountains, Bombana Regency, Southeast Sulawesi. There are three generations of veins identified including 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. Temperature of homogenization (Th) and salinity at Rumbia Mountain of the first vein vary from 220 to 355.30oC and 6.74 to 10.11 wt. % NaCl eq., respectively. The second generation vein was originated at Th of 157 to 255.50oC and salinity of 3.39 to 6.88 wt.%NaCl eq., whereas the third generation vein formed at lowest Th varying from 104.40 to 265.90oC and less saline fluid at salinity range between 0.18 and 6.30 wt.% NaCl eq. The result of temperature formation value correlation to the depth of the formation of orogenic gold deposits in Rumbia Mountain is indicated to form on sub-greenschist to greenschist facies at depth of about 4-8 kilometers and formation temperature between 104.40 - 355.30oC at zone epizonal and mesozonal. Based on characteristics fluids inclusion discussed above, the primary metamorphic-hosted gold mineralization type at Rumbia Mountain tends to meet the criteria of orogenic gold type. Keyword : fluid iclusion, quartz veins, Rumbia mountain, orogenic gold deposits.

Geochemical, stable isotopic (S, O, H, C), microthermometric and geochronological (U-Pb) evidence on the genesis of the Pınarbaşı porphyry Cu-Mo mineralization (Gediz-Kütahya, Western Turkey)

The Pınarbaşı porphyry CuMo mineralization is located at northwest of Gediz (Kütahya-Turkey) and east of Simav (Kütahya-Turkey) in western Anatolia. The Pınarbaşı CuMo mineralization is hosted by Pınarbaşı granitoidic intrusion consisting of granite, granodiorite and quartz monzonite. Geochemical and geochronological evidences for Pınarbaşı granitoidic rocks show that they are high-K calc-alkaline, and I-type granitoid magma likely developed post-collisional extensional regime. The UPb zircon age of granite (18.88 ± 0.17 Ma) and quartz monzonite porphyry (18.27 ± 0.14) obtained from the Pınarbaşı granitoid show Early Miocene (Burdigalian). The Pınarbaşı CuMo mineralization predominantly comprises molybdenite, chalcopyrite, galena, sphalerite, pyrite, fahlore, magnetite, bornite, hematite, jarosite, malachite and orpiment occurred in disseminated form in veins/veinlets associated with potassic, phyllic (sericitic) and advanced argillic alteration zones. According to the paragenetic and crosscutting relationships of veins/veinlets, the ore-forming process were divided into three stages; early-stage: quartz – molybdenite ± K-feldspar ± pyrite veins associated with potassic alteration, middle-stage: quartz ± calcite ± chalcopyrite ± galena ± sphalerite ± molybdenite + pyrite veins in phyllic alteration and late-stage: quartz ± calcite ± pyrite veins associated with advanced argillic alteration. Three types of fluid inclusions in quartz distinguished were designated as L-rich L + V phases (Type-I), salt-bearing L + V + S (Type-II), and V-rich L + V phases (Type-III). FIs of the early and middle stages are predominantly Type-II and Type-III inclusions, whereas the late-stage minerals commonly contain Type-I inclusions. Homogenization temperatures and salinities of FIs trapped in the early-stage quartz range from 481 to 590 °C and 13.19 to 61.1 wt% NaCl equivalent, respectively. FIs in quartz of the middle-stage yield homogenization temperatures (Th) of 310 to 460 °C, while halite dissolution temperatures are ranged from 264 to 430 °C, and salinities of 7.9 to 50.3 wt% NaCl eq. Homogenization temperatures and salinities of FIs in calcite of the middle-stage are range from 270 to 420 °C, 3.4 to 49.1 wt% NaCl eq. The late-stage homogenize at temperatures of 138 to 240 °C, and salinities of 0.9 to 6.5 wt% NaCl eq. The δ34SH2S values (0.6 to 4.5‰) of sulfides (molybdenite, chalcopyrite, pyrite and galena) and the δ18OSMOW (6.9 to 9.6‰) - δD (−71 to −86‰) values of molybdenite-bearing quartz from Pınarbaşı CuMo mineralization suggest a magmatic origin for the ore-forming fluids. The δ13CPDB (from −4.65‰ to 0.55‰) and δ18OSMOW (from 9.05‰ to 18.76‰) values of calcite which is one of the most common gangue minerals in Pınarbaşı mineralization show a high temperature influence and/or sedimentary contamination process to magmatic carbonate as well as continental carbonate. The S–O–H–C and UPb isotopic compositions indicate that the metallic elements and fluids came primarily from a magmatic source linked to Miocene intrusion. The geological, geochronological, and geochemical data support a magmatic-hydrothermal origin for the Pınarbaşı CuMo mineralization and confirm that mineralization is formed from an Early Miocene porphyry-related magmatic-hydrothermal system that is genetically linked with Eğrigöz and Pınarbaşı granitoids.

Genesis of the Koka Gold Deposit in Northwest Eritrea, NE Africa: Constraints from Fluid Inclusions and C–H–O–S Isotopes

The Koka gold deposit is located in the Elababu shear zone between the Nakfa terrane and the Adobha Abiy terrane, NW Eritrea. Based on a paragenetic study, two main stages of gold mineralization were identified in the Koka gold deposit: (1) an early stage of pyrite–chalcopyrite–sphalerite–galena–gold–quartz vein; and (2) a second stage of pyrite–quartz veins. NaCl-aqueous inclusions, CO2-rich inclusions, and three-phase CO2–H2O inclusions occur in the quartz veins at Koka. The ore-bearing quartz veins formed at 268 °C from NaCl–CO2–H2O(–CH4) fluids averaging 5 wt% NaCl eq. The ore-forming mechanisms include fluid immiscibility during stage I, and mixing with meteoric water during stage II. Oxygen, hydrogen, and carbon isotopes suggest that the ore-forming fluids originated as mixtures of metamorphic water and magmatic water, whereas the sulfur isotope suggests an igneous origin. The features of geology and ore-forming fluid at the Koka deposit are similar to those of orogenic gold deposits, suggesting that the Koka deposit might be an orogenic gold deposit related to granite.

Ore-Fluid Evolution of the Sizhuang Orogenic Gold Deposit, Jiaodong Peninsula, China

The Sizhuang gold deposit with a proven gold resource of &gt;120 t, located in northwest Jiaodong Peninsula in China, lies in the southern part of the Jiaojia gold belt. Gold mineralization can be divided into altered rock type, auriferous quartz vein type, and sulfide-quartz veinlet in K-feldspar altered granite. According to mineral paragenesis and mineral crosscutting relationships, three stages of metal mineralization can be identified: early stage, main stage, and late stage. Gold mainly occurs in the main stage. The petrography and microthermometry of fluid inclusion shows three types of inclusions (type 1 H2O–CO2 inclusions, type 2 aqueous inclusions, and type 3 CO2 inclusions). Early stage quartz-hosted inclusions have a trapped temperatures range 303–390 °C. The gold-rich main stage contains a fluid-inclusion cluster with both type 1 and 2 inclusions (trapped between 279 and 298 °C), and a wide range of homogenization temperatures of CO2 occurs to the vapor phase (17.6 to 30.5 °C). The late stage calcite only contains type 1 inclusions with homogenization temperatures between 195 and 289 °C. With evidences from the H–O isotope data and the study of water–rock interaction, the metamorphic water of the Jiaodong Group is considered to be the dominating source for the ore-forming fluid. The ore-fluid belonged to a CO2–H2O–NaCl system with medium-low temperature (160–360 °C), medium-low salinity (3.00–11.83 wt% NaCl eq.), and low density (1.51–1.02 g/cm3). Fluid immiscibility caused by pressure fluctuation is the key mechanism in inducing gold mineralization in the Sizhuang gold deposit.

Relation Between Fracture Stability and Gas Leakage into Deep Aquifers in the North Perth Basin in Western Australia.

The Kockatea Shale is a proposed target for unconventional gas development in the North Perth Basin in Western Australia. This research is concerned with correlating the extent of thermogenic gas leakage into deep aquifers overlying the Kockatea Shale with an assessment of how close the formation is to mechanical failure. Data from two petroleum exploration wells located approximately 20 km apart were considered. Both have comparable stratigraphy; however, they differ by their local tectonic setting. The stress regime is strike slip at Arrowsmith 2 well and for an assumed hydrostatic pressure the Kockatea Shale is not close to frictional limits. Minor amounts of methane and trace amounts of short chain alkanes are leaking into deep aquifers pre‐development. In contrast, the stress regime is strike slip/normal at Woodada Deep well and the Kockatea Shale is close to frictional limits. Significant volumes of gas including methane and condensate are leaking into deep aquifers. The sealing capacity of the Kockatea Shale as evidenced by the variation in gas concentration in aquifers at the two sites indicates the formation is sensitive to stress. Additionally given the low permeability of the regional Kockatea Shale seal, it is assumed that at both locations gas leakage is via critically stressed faults. Deep aquifers proximal to the shale gas target are low salinity (<5000 ppm NaCl eq.) at Woodada Deep well and are saline at Arrowsmith 2 well. Based on this assessment, it is suggested that hydraulic fracture stimulation at the Woodada Deep well poses a significant environmental risk.

The polymetallic magmatic-hydrothermal Xiangdong and Dalong systems in the W–Sn–Cu–Pb–Zn–Ag Dengfuxian orefield, SE China: constraints from geology, fluid inclusions, H–O–S–Pb isotopes, and sphalerite Rb–Sr geochronology

Vein-type deposits, including the Xiangdong W–Sn and Dalong Pb–Zn deposits, occur in or near the Dengfuxian composite granite pluton, comprising predominantly Triassic and minor Jurassic intrusions. Liquid-rich NaCl-aqueous inclusions, vapor-rich NaCl-aqueous inclusions, liquid-rich CaCl2-NaCl-aqueous inclusions, two-phase CH4-rich inclusions, three-phase CO2-H2O inclusions, and three-phase calcite-bearing inclusions occur in the quartz veins at Xiangdong, whereas only liquid-rich NaCl-aqueous inclusions occur at Dalong. The Xiangdong veins formed at temperatures near 241 °C, from NaCl-CaCl2-H2O-CH4-CO2 fluids averaging 11.4 wt% NaCl eq. The Dalong deposit formed at temperatures near 186 °C from NaCl-H2O(-CH4) fluids averaging 6.2 wt% NaCl eq. The ore-forming mechanisms at Xiangdong include fluid immiscibility during stage I, fluid mixing during stage II, and mixing with meteoric water accompanied by cooling during stage III. The ore-forming mechanisms at Dalong include cooling and mixing with meteoric water. Oxygen and hydrogen isotopes suggest that the ore-forming fluids from both deposits originated as mixtures of magmatic water with various amounts of meteoric water. Sulfur and strontium isotopes suggest an igneous origin for both deposits and possibly mixing with S and Sr from sedimentary rock for Dalong. Lead isotopes indicate that ore metals originated mainly from the upper crust with minor mantle contributions. Sphalerite from Dalong gives a Rb-Sr isochron age of 151.6 ± 7.1 Ma, consistent with the mineralization age of Xiangdong. Both the W–Sn and Pb–Zn ore-forming events are closely related to Late Jurassic magmatism, which occurred in an environment of lithospheric extension and thinning.

Geology and Geochemistry of the giant Huoshaoyun zinc-lead deposit, Karakorum Range, northwestern Tibet

The recently discovered giant Huoshaoyun zinc-lead deposit in the Karakorum Range, northwestern Tibet, China, consists of a major zinc-lead carbonate and a minor lead-dominant sulfide mineralization with metal reserves of zinc and lead of over 16 million tonnes. The zinc-lead carbonate mineralization is composed of smithsonite and cerussite, with laminated, massive, veined and botryoidal textures, showing sedimentary and metasomatic structures. The lead-dominant sulfide mineralization is composed mainly of galena and minor sphalerite and pyrite, with laminated, brecciated, and veined textures. The laminated sulfide mineralized zones occur at the top of the deposit, whereas the zinc-lead carbonate mineralized bodies are located below the sulfide zones. Lead-dominant sulfide veins cut the zinc-lead carbonate ores and the host limestone. The sequence of formation of the lead-zinc ores with various mineral colors in thin sections is as follows: (1) light-colored to yellowish, fine- to coarse- and subhedral to euhedral smithsonite; (2) yellowish to reddish, fine- to coarse- and subhedral to euhedral smithsonite; (3) light-colored veined smithsonite; (4) white coarse-grained, xenomorphic cerussite; (5) colorless euhedral to sub-angular quartz crystals; (6) euhedral to anhedral lead-zinc sulfides and gypsum. The mineralization events of the Huoshaoyun deposit are: (1) early hydrothermal sedimentary smithsonite mineralization; (2) hydrothermal replacive smithsonite mineralization; (3) vein-type smithsonite mineralization; (4) open space filling and replacive cerussite mineralization; (5) lead-zinc sulfide mineralization. The fluid inclusions of cerussite indicate that the hydrothermal fluids of the cerussite ore-forming stage are characterized by a temperature range of at least 186–206 °C and low salinities (0.7–1.2 wt% NaCl eq.). The source of oxygen and carbon for the zinc-lead carbonate mineralization is possibly consistent with the involvement of marine water and a magmatic fluid, and is probably dominated by the magmatic fluid. The source of sulfur for the lead-dominant sulfide mineralization is possibly related to a magma reservoir. The zinc-lead-carbonate portion of the deposit represents a primary hypogene non-sulfide mineralization.

Fluid Inclusion and H-O Isotope Geochemistry of the Phapon Gold Deposit, NW Laos: Implications for Fluid Source and Ore Genesis

The Phapon gold deposit, located in northern Laos, is a unique large-scale gold deposit in Luang Prabang-Loei metallogenic belt. It is hosted in the Lower Permian limestone and controlled by a NE-trending ductile-brittle fault system. There are three types of primary ore including auriferous calcite vein type, disseminated type, and breccia type, and the first two are important in the Phapon gold deposit. Based on fluid inclusion petrography and microthermometry, three types of primary fluid inclusions including type 1 liquid-rich aqueous, type 2 vapor-rich aqueous and type 3 daughter mineral-bearing aqueous were identified in hydrothermal calcite grains. The ore-forming fluids are normally homogeneous, as indicated by the widespread type 1 inclusions with identical composition. The coexistence of type 1 and type 2 inclusions, showing similar final homogenization temperature but different compositions, indicate that fluid immiscibility did locally take place in both two types of ores. The results of microthermometry and H-O isotopes geochemistry indicate that there are little differences on ore-fluid geochemistry between the auriferous calcite vein-type and disseminated type ores. The oreforming fluids are characterized by medium-low temperatures (157—268 °C) and low salinity (1.6 wt.%-9.9 wt.% NaCl eq.). It is likely to have a metamorphic-dominant mixed source, which could be associated with dehydration and decarbonisation of Lower Permian limestone and Middle-Upper Triassic sandstones during the dynamic metamorphism. The fluid-wallrock interaction played a major role, and the locally occurred fluid-immiscible processes played a subordinate role in gold precipitation. Combined with the regional and ore deposit geology, and ore-fluid geochemistry, we suggest that the Phapon gold deposit is best considered to be a member of the epizonal orogenic deposit class.