جستجوی مقالات مرتبط با کلیدواژه « جوشش » در نشریات گروه « زمین شناسی »

One of the common processes that lead to the formation and enrichment of precious metal deposits is boiling. The existence of a spatial relation between fluid boiling and deposition of precious metals is a valuable tool in exploration of epithermal deposits. Therefore, the investigating of the process occurrence in epithermal deposits will be able to predict the continuation of exploration trend. Chah-Morad epithermal gold deposit is located in 75 km northwest of Bazman in the Sistan and Baluchistan Province and in the Makran-Chagai Magmatic Arc southeast of Iran. The mineralization in the Chah-Morad deposit occurred in 3 stages and in quartz veins that exist between the altered argillic alteration zone and dacite and rhyodacite sub-volcanic rocks. Textural mineralogical and fluid inclusions studies indicate the occurrence of the boiling process in this deposit. The most important kinds of evidence for the occurrence of this process are: a) the presence of adularia, b) platy calcite texture, c) breccia, crustiform-colloform textures, d) different liquid-vapor ratios of fluid inclusions, e) the increase in the salinity of fluid inclusions with the decrease in homogenization temperatures, f) the coexistence of fluid inclusions with different salinities and g) co-existing liquid single-phase fluid inclusions with vapor single-phase fluid inclusions. Therefore, the existance of boiling is confirmed in the Chah-Morad deposit.

Shadan gold deposit is located 60 km southwest of Birjand and north of Lut block. the Eocene post-collision magmatism resulting from the subduction of the Sistan Ocean has played a role in the formation of the Shadan gold deposit. Gold mineralization in Shadan deposit is directly related to the emplacement of plutonic and sub volcanic plutons with a composition diorite to monzodiorite that intruded into andesite-pyroclastic units. The main alterations in the area are primary potassic and propylitic alterations, the first of which is located in the center of the hydrothermal-magmatic system and the second of which surrounds the potassic alteration. These two alterations are overprinted by the late Phyllic and Argillic alterations. Mineralization in Shadan deposit occurred in the form of stockwork, vein-veinlets, disseminated and hydrothermal breccias and the most important trigger of gold mineralization in this deposit was Shadan pluton. According to SEM studies, the most important host of gold in the hypogene part is pyrite and gold occurs as native, electrum and calavarite. The most characteristic veins of Shadan gold deposit are M and A type and banded veins. Shadan pluton contains abundant hornblende phenocrysts and biotite as well as high amounts of magnetite in various alterations which can indicate the presence of a highly oxidized magma with high amounts of water. Based on all the mentioned evidences as well as the Cu / Au ratio (3000), Shadan deposit can be introduced as the first gold-rich porphyry deposit in Iran.

The Mazraeh Shadi is located about 130 km northeast of Tabriz (NW Iran) in the Arasbaran metallogenic belt. The deposit occurs as a series of veins within the Eocene andesites. Mineralization shows epithermal system that controlled by fault distribution. Epithermal textures within the veins include comb, vaggy quartz, cockade, boxworke, plate calcite and breccia. Pyrite is the main ore mineral associated with chalcopyrite, chalcocite, covellite, sphalerite, galena and gold. The result of geochemistry on the small rock samples from silica veins shows values of gold (max17100 ppb), Pb(max 21100 ppm), Ag(max 9.43ppm), Cu(max 611ppm) and Zn (max 333 ppm). Microthermometric studies were conducted on quartz samples from silicified and mineralized zones and provides substantial micro-thermometric data for a new interpretation. Fluid inclusions generally occur in range from 5 to 90 μm in size. Three types of fluid inclusions are typically observed at Mazraeh Shadi:(1) liquid-rich two-phase, (2) vapour-rich two-phase (3) vapour-rich mono-phase. The homogenization temperatures of all inclusions from 160 to 324 °C and the average of homogenization temperature is 228°C .The salinities are 0.17–5.1 wt.% NaCl equiv. The last ice-melting temperature is between –2.2 and -3.2°C. All fluid inclusions are plotted into the epithermal box and into the region between the primary magmatic water box and the meteoric water. Mineralization of Au is the result of pyrite precipitation, dilution- mixing of an oxidized meteoric water decreasing of pH, boiling and fluid mixing and there are two fluids participated in the formation of Mazraeh Shadi deposit. Fluid inclusion data shows the depth of mineralization at Mazraeh Shadi deposit probably ranged from 230 m to 380 m below the paleosurface and three-dimensional graphs confirm the deposition of lead and zinc in with high temperature-low salinity fluid and deposition of gold with low temperature-high salinity fluid. The zoning pattern shows clearly base metals such as Cu, Pb, Zn and Mo occur at the deepest levels, whereas precious metals occur at higher elevations with respect to base metals due to boiling of hydrothermal fluids in epithermal system.

A wide variety of world-class porphyry Cu deposits occur in the Urumieh-Dohktar magmatic arc (UDMA) of Iran.The arc is composed of calc-alkaline granitoid rocks, and the ore-hosting porphyry intrusions are dominantly granodiorite to quartz-monzonite (Zarasvandi et al., 2015). It is believed that faults played an important role in the emplacement of intrusions and subsequentporphyry-copper type mineralization (Shahabpour, 1999). Three main centers host the porphyry copper mineralization in the UDMA: (1) Ardestan-SarCheshmeh-Kharestan zone, (2) Saveh-Ardestan district; in the central parts of the UDMA, hosting the Dalli porphyry Cu-Au deposit, and (3) Takab-Mianeh-Qharahdagh-Sabalan zone. Mineralized porphyry coppersystems in the UDMA are restricted to Oligocene to Mioceneintrusions and show potassic, sericitic, argillic, propylitic and locally skarn alteration (Zarasvandi et al., 2005; Zarasvandi et al., 2015). In the Dalli porphyry deposit, four hydrothermal alteration zones, includingpotassic, sericitic, propylitic, and argillic types have been described in the two discrete mineralized areas, namely, northern and southern stocks. Hypogenemineralization includes chalcopyrite, pyrite, and magnetite, with minor occurrences of bornite.Supergene activity has produced gossan, oxidized minerals and enrichment zones. The supergene enrichment zone contains chalcocite and covellite with a 10-20 m thickness. Mineralization in the northern stock is mainly composed of pyrite and chalcopyrite. The aim of this study is the investigation and classification of hydrothermal veins and the constraining of physicochemical compositions of ore-forming fluids using systematic investigation of fluid inclusions. Twenty samples were collected from drill holes. Thin and polished sections were prepared from hydrothermal veins of thepotassic, sericitic and propylitic alteration zones. Samples used for fluid inclusion measurements were collected from drill cores DH01, DH02, DH06, and DH07, and outcrop samples. Microthermometric data were obtained by freezing and heating of fluid inclusions on a Linkam THMSG600 mounted on an Olympus microscope at Lorestan University. 1) Five main veintypes were identified, belonging to three stages of mineralization:type (I): barren quartz, type (II): quartz + pyrite + chalcopyrite ± bornite ± chalcocite ± covelite, type (III): quartz + magnetite ± chalcopyrite, type (IV): K-feldspar± quartz ± chalcopyrite, type (V): chlorite + biotite. 2) Seven groups of fluid inclusionswere observed: (IA) liquid-rich mono-phase, (IB) vapor-rich mono-phase, (IIA) liquid-rich two-phase (liquid + vapor), (IIB) vapor-rich two-phase (vapor + liquid), (IIIA) high salinity simple fluids (liquid + vapor + halite), (IIIB) high salinity opaque mineral-bearing fluids (liquid + vapor + halite + pyrite + chalcopyrite + hematite), (IIIAB) multi-phase fluids (liquid + vapor + halite + sylvite + hematite + magnetite + pyrite + chalcopyrite ± erythrosiderite) 3) Multiphase fluid inclusions with predominant homogenization temperatures 420 to 620˚C and predominant salinities 70 to 75 wt.%NaCl, are thought to be the early fluids involved in mineralization. 4) The coexistence of high saline liquid and vapor rich fluid inclusions (IIIAB, IIIB, IIIA and IIA types) resulted either from fluid entrapment during the boiling process or the co-presence of two immiscible fluids generated from the magma. 5) Dalliporphyry Cu-Au deposit was formed in a magmatic-meteoric system. Two conventional thermometric procedures, freezing and heating, were employed for the measurement of temperature of homogenization and approximate salinity. Freezing was conducted mainly for halite-under saturated inclusions (types IIA and IIB), to measure the initial melting temperature (Te) and the last melting point (Tmice), whereas heating was carried out on the halite-bearing inclusions (types IIIA, IIIB and IIIAB). Based on the microthermometric results, the Dalli fluid inclusions can be divided into two distinct groups: (1) medium-high temperature, hypersaline (Types IIIA, IIIB and IIIAB) and (2) low-medium temperature, low salinity group (Types IIA and IIB). Type IIB inclusions, which homogenize to the vapor phase and have a relatively low cooling rate, provide a fairly good estimate of entrapment pressure (Roedder and Bodnar, 1980). Based on the pressure estimated for the Dalli deposit, mineralization likely occurred at depth of 0.6-1.1 km. The calculated depth is coincident with the estimated mineralization depths of the porphyry deposits in the world (Pirajno, 2009). Fluid inclusions with a wide range of vapor and liquid ratios are abundant in all of the Dalli samples. This represents heterogeneous trapping of liquid and vapor. The coexistence of inclusions with different volumes of vapor contents, which homogenize either to liquid (Th(L-V)) or vapor (Th(V-L)), are interpreted as an evidence for the prevailing wide range of physico-chemical conditions during the cooling history of ore-forming fluid at the Dalliporphyry Cu-Au deposit. The boiling process is documented by the abundance of heterogeneously trapped fluid inclusions with extremely variable liquid to vapor ratios (Ahmad and Rose, 1980). Acknowledgements: We thank of ShahidChamran University of Ahvaz for their support and moreover, Lorestan University for microthermometric studies.

The Argash antimony ore deposit is located at south of Neyshabour and the eastern part of the Sabzevar zone. This deposit occurs within a sequence of Eocene-Oligocene volcanic-intrusion rocks. The mineralization occurs as open space filling, taking place as irregular veins, veinlets and hydrothermal breccias. The mineralogy of the veins is comparatively simple. The primary antimony-bearing mineral is stibnite. Other sulfides have been found in association with stibnite are pyrite, chalcopyrite and sphalerite. Quartz, illite, adularia, chlorite, epidote and kaolinite are the main hydrothermalg gangue minerals occurring around the veins. Hydrothermal alteration is zoned around the veins and consists of three major types including silicification within the immediate veins, argillic alteration enveloping the veins, and propylitic alteration distal to the veins. The intensity of silicification and argillic alteration decreases with depth and away from the veins. The evaluation of the geochemical data set based on multivariate statistical analyses indicates positive correlation between Zn, Ag, As and Sb and the same distribution pattern of these elements in the boreholes. The mineralogic, alteration and geochemical characteristics of the studied area and comparison with epithermal ore deposits indicate that the Arghash quartz-antimony veins represent an epithermal system of the low-sulfidation type. This data suggests that boiling and cooling were the main ore deposition processes in the area.