جستجوی مقالات مرتبط با کلیدواژه « intermediate-sulfidation epithermal » در نشریات گروه « زمین شناسی »

Kourcheshmeh Pb-Zn-Cu deposit is located 40 km southwest of Takestan (Qazvin province) and west of the Mardabad-Bouinzahra volcanic belt. The mineralization occurred as Pb-Zn-Cu-bearing quartz veins hosted by early-middle Eocene tuff and lava strata and show a close spatial relationship with the middle Eocene pyroxene quartz monzodiorite body. The main ore vein ranges from 70 to 200 meters long, and 0.5 to 2 meters thick. Pyrite, chalcopyrite, galena, sphalerite, and tennantite-tetrahedrite, accompanied by minor pyrolusite and psilomelane, are the main ore minerals; quartz, calcite, siderite, barite, and sericite-illite are gangue minerals. Goethite, cerussite, smithsonite, malachite, and covellite are formed by supergene processes. The ore minerals formed as disseminated, vein-veinlets, brecciated, comb, crustiform, colloform, plumose, and vug infill textures. Six stages of mineralization can be distinguished at Kourcheshmeh, where Pb-Zn-Cu mineralization occurred as quartz-pyrite-chalcopyrite-galena-sphalerite ± tennantite-tetrahedrite veins and breccias in the second stage. Wall-rock alteration comprises silicification, intermediate argillic, carbonate, and propylitic alteration. Chondrite–normalized trace elements and REE patterns of ore samples, pyroxene quartz monzodiorite body, and fresh host acidic crystal tuff are comparable. This specifies that alteration and leaching of elements from the host volcanic rocks are involved in mineralization. Features of the Kourcheshmeh Pb-Zn-Cu deposit are similar to the intermediate-sulfidation type of epithermal deposits.

Tozlou Pb-Zn mineralization, ~250-300m long, and ~50m thick, is hosted by limestone units of the Qom Formation. The main mineralization zone occurred as vein-veinlets and vug infill textures, where mineralization is observed as Pb-Zn-bearing barite veins or supergene minerals (cerussite and smithsonite). Mineralization at Tozlou can be divided into five stages. Stage 1 is the decarbonatization of the limestone host rock, which is characterized by the increased porosity and permeability of the host rock. Stage 2 is categorized with dolomitization processes along with minor pyrite. Stage 3 occurred as Pb-Zn-bearing barite and calcite (calcite II) veins. Stage 4 includes late-stage calcite (calcite III) veins. Stage 5 is related to supergene processes. Hydrothermal alterations include decarbonatization, carbonatization ± silicification, and late carbonatization. Ore minerals include galena and pyrite along with minor sphalerite. Calcite, barite, and quartz are gangue minerals. Smithsonite, cerussite, and goethite are formed by supergene processes. The ore minerals show vein-veinlets, brecciated, disseminated, vug infill, colloform, cockade, replacement, and residual textures. The Chondrite-normalized rare earth elements pattern of ore samples, fresh and altered limestones is similar, which can indicate the major role of host rocks in the concentration of ore-forming elements. This pattern is almost similar for different ore samples, which can indicate that they have been formed by the same mineralization system. Characteristics of Tozlou occurrence are comparable with intermediate-sulfidation type of epithermal deposits.

Epithermal deposits are a group of base/precious-metal deposits that are formed by hydrothermal fluids in shallow environments under pressure/temperature changes and fluid-rock interactions (Hedenquist et al., 2000). Based on the host rock, epithermal deposits are divided into volcanic-hosted deposits and sedimentary-hosted deposits. According to the tectonic setting and magma type, they are divided into calc-alkaline magmas (including three subcategories of high-, intermediate-, and low-sulfidation) and alkaline magmas (White and Hedenquist, 1990; Cooke and Simmons, 2000; Hedenquist et al., 2000; Simmons et al., 2005). These types of deposits include a continuous range of deposits formed by magmatic/meteoric fluids and show different geometry, but have the same formation mechanism, especially the hydrothermal fluids circulation (Sillitoe and Hedenquist, 2003; Simmons et al., 2005).
Sedimentary rock-hosted deposits are divided into two groups: Carlin-type and sediment-hosted disseminated deposits. Carlin-type deposits are often formed as strata-bound or replacements at the boundary of rock units and are controlled by faults. They are distinguished by invisible Au in As-rich pyrite and arsenopyrite and do not show compatible spatial relationships to magmatic centers (Kuehn and Rose, 1992). Sediment-hosted disseminated deposits occurred as disseminated ore in sedimentary rocks (Hofstra and Cline, 2000). These deposits are physically and chemically comparable to Carlin-type deposits, but spatially and temporally are related to sub-volcanic porphyry intrusions (Theodore et al., 2000; Hofstra and Cline, 2000).
Tozlou Pb-Zn occurrence is 50km south of Qeydar in Zanjan province. This occurrence was first discovered/explored in 2017. Although general geological characteristics of Tozlou occurrence have been determined (Majidifard and Shafei, 2006), the mineralogy and origin of Tozlou occurrence have not been studied in detail. Here, detailed geology, mineralogy, alteration styles, and geochemistry of Tozlou occurrence are investigated to constrain the genetic model and type of its mineralization system. These results may have implications for future exploration of base-metal mineralization in this region and nearby areas. 

Comprehensive field and laboratory works have been carried out on Tozlou area. During the fieldwork, a detailed stratigraphic section of limestone units of Qom Formation was measured, sampled, and described. Fifty samples were collected from ore zones and limestone host rocks for laboratory analysis. Then, 34 thin and 15 polished-thin sections were prepared for mineralogical studies in the laboratory at the University of Zanjan, Iran. Fourteen typical samples from the ore zones and fresh/altered host limestone were analyzed for geochemical analysis using ICP–MS in Zarazma Analytical Laboratories, Tehran, Iran.

The main rock units exposed in Tozlou occurrence belong to Eocene sequence, Lower Red Formation, Qom Formation, and Quaternary units. Small outcrops of gabbro-gabbro diorite (gb) can also be seen in this region. Eocene strata include brown thin-bedded sandstone (Unit Es), alternating tuff and shale (Unit Etsh), and thin- to medium-bedded tuffs (Unit Et). Lower Red Formation includes a polygenetic conglomerate (Unit Ollrc) of Oligocene age. Qom Formation consists of massive- to medium-bedded cream-to-grey limestones (Unit OMql) and alternating marl and thin-bedded grey limestone (Unit OMqml). Quaternary units include terrigenous sediments.
Pb-Zn mineralization at Tozlou has ~250-300 m leng and ~50 m thick and is hosted by limestone units of Qom Formation. The main mineralization zone occurred as vein-veinlets and vug infill textures, where mineralization is observed as Pb-Zn-bearing barite veins or supergene minerals (cerussite and smithsonite). Decarbonatization, carbonatization±silicic, dolomitization, and late carbonatization are hydrothermal alterations in Tozlou area. Mineralization processes at Tozlou can be divided into five stages. Stage 1 comprises the decarbonatization of the limestone host rock, which is characterized by the increased porosity and permeability of the host rock. Stage 2 is represented by the dolomitization of the limestone host rock, which is accompanied by minor pyrite. Stage 3 occurs as Pb-Zn-bearing barite and calcite (calcite II) veins. Stage 4 is characterized by late-stage calcite (calcite III) veins. Stage 5 is related to supergene processes.
Ore minerals include galena and pyrite along with minor sphalerite. Calcite, barite, and quartz are gangue minerals. Smithsonite, cerussite, and goethite are formed by supergene processes. The ore minerals show vein-veinlets, brecciated, disseminated, vug infill, colloform, cockade, replacement, and residual textures. The Chondrite-normalized rare earth elements patterns of ore samples, fresh and altered limestones, are similar, which can indicate the major role of host rocks in the concentration of ore-forming elements. This pattern is almost similar for different ore samples, which can indicate that they have been formed by the same mineralization system. Despite carbonate host rock, we think that mineralization at Tozlou is similar to the intermediate-sulfidation style of epithermal base metal deposits.

Bijvard prospect area is located in the northern part of Central Iran zone, Sabzevar zone, about 40 km north of Bardaskan. The rock units exposed in the area include Cretaceous volcano-sedimentary rocks (andesite, basalt, graywacke and conglomerate) that syenogranite porphyry unit has intruded into them.  Mineralization has structural control, with N35E trending, and has altered the andesitic rock unit. Mineralization in this area has occurred in two parts: 1- Gold-bearing ores, that are mostly associated with silica and argillic alterations within gossan zone, which is surrounded by propylitic alteration 2- Manganese mineralization has occurred within gray wacke unit. Mineralogy is simple and primary minerals are pyrite, chalcopyrite, pyrolusite and braunite and secondary minerals include goethite, hematite, covellite, chalcocite, malachite and various Mn-bearing minerals. Quartz and clay minerals associated with minor calcite are the most important gangue minerals. The maximum value of gold is 1.4 ppm and the minimum value of gold is 0.01 ppm. In addition, the amount of copper is ranging between 88 ppm and 2.2%, arsenic is 21 to 100 ppm, and zinc is 162 to 495 ppm. Based on tectonic setting, host rock, structural control, type of alteration and the absence of high and low sulfide index minerals, Bijvard prospect area is probably an intermediate sulfidation epithermal type.