Exploration and Mining
Kamran Mostafaei; Mohammadnabi Kianpour; Mahyar Yousefi
Abstract
This article is devoted to introducing a novel application of the Gray Wolf Optimizer in one of the most challenging issues related to mineral exploration, anomaly separation from the background in stream sediment geochemical studies. The Alut geological sheet, located in the Sanandaj-Sirjan zone, which ...
Read More
This article is devoted to introducing a novel application of the Gray Wolf Optimizer in one of the most challenging issues related to mineral exploration, anomaly separation from the background in stream sediment geochemical studies. The Alut geological sheet, located in the Sanandaj-Sirjan zone, which has special importance to gold prospecting, has been studied for the distribution of gold and arsenic that accompany each other as the paracenteses in such deposits. The cost function used in this algorithm has been provided according to previously well-explored deposits. While the GWO algorithm was able to divide the sheet into two classes of anomalous and non-anomalous areas, the fractal method identified four categories among distributions of gold and arsenic, which impose the responsibility of selecting anomalous areas on the scientists. Obviously, the GWO draws the areas as potential zones of prospecting that may be neglected by fractal strategy. The derived results show that 24.8ppm and 15.7ppb is anomaly threshold for arsenic and gold distribution respectively. The comparison of the results shows that the anomaly threshold obtained by the fractal methods and GWO algorithm for arsenic is almost the same, but the anomaly threshold for gold in the GWO algorithm method is optimal.
Economic Geology
Pooya Seyed Salehi Naeini; Saeid alirezaei
Abstract
The Kharestan-Bidester area, northwest of the Taftan volcano, is covered by a series of Plio-Quaternary lava flows and pyroclastic materials. The area is marked by extensive silicic and argillic alterations. The silicic zones, distinguished by vuggy texture, are bordered by advanced-intermediate argillic ...
Read More
The Kharestan-Bidester area, northwest of the Taftan volcano, is covered by a series of Plio-Quaternary lava flows and pyroclastic materials. The area is marked by extensive silicic and argillic alterations. The silicic zones, distinguished by vuggy texture, are bordered by advanced-intermediate argillic alterations. They occur as linear features across faults and fractures, as well as massive bodies of variable sizes, and are comparable, at regional scale, to lithocaps developed in the upper parts of the porphyry systems. The silicic-argillic zones are mineralized with gold at variable grades. Gold occurs mostly as submicroscopic particles of electrum and native gold. Pyrite, variably oxidized at surface and shallow levels, is the main metallic mineral, associated with trace sulfosalts, tetrahedrite and enargite. Minor malachite staining locally occurs in the ore zones. The geologic setting, hydrothermal alteration, ore mineralogy and texture/structure allow the Kharestan-Bidester to be compared with high-sulfidation epithermal systems.
Economic Geology
Kourosh Shabani; Nima Nezafati; Morteza Momenzadeh; Mohammad Hashem Emami; Seyed Jamal Shaykhzakaryaii
Abstract
The Tareek Darreh gold Gold & Copper deposit is located 40km north of Torbat- e Jam in the Khorasan-Razavi province,NE-Iran. The study area is mainly comprised of slightly metamorphosed, sedimentary rocks of Jurassic age including alternation of shale, siltstone, and sandstone. These rocks have been ...
Read More
The Tareek Darreh gold Gold & Copper deposit is located 40km north of Torbat- e Jam in the Khorasan-Razavi province,NE-Iran. The study area is mainly comprised of slightly metamorphosed, sedimentary rocks of Jurassic age including alternation of shale, siltstone, and sandstone. These rocks have been intruded by plutonic rocks such as gabbronorite, diorite, quartz-diorite, and rhyodacite. The ore bodies are exposed by trenching and pitting. The alteration minerals quartz, chlorite, albite, and sericite which are observed mostly on the top or margin of the stocks. Alteration is more intensive at the contacts of the stocks where vein type mineralization has occurred. The veins are mainly composed of silica type and calcite type, arsenopyrite, chalcopyrite, and pyrite main ore minerals. Probably more than 2-stages telescopic mineralization occurred in these zones and the conditions of temperature and pressure, as seen below. Appears to be a continuation of tectonic activity in the same place as intrusive and a little later the main cause of this phenomenon. According to our studies, The Tareek Darreh gold deposit is considered to be similar to the "intrusion-related gold "type.
Exploration and Mining
Ghodratollah Rostami Paydar; Hani Asadi Hoveizian
Abstract
Determination of relationship between rock mass properties concerning to rock qualification design (RQD) has an important role in mine planning and designation. The aim of this study is separation of rock mass properties to designing the mine planning based on the 3267 RQD data analysis of 43 drill-core ...
Read More
Determination of relationship between rock mass properties concerning to rock qualification design (RQD) has an important role in mine planning and designation. The aim of this study is separation of rock mass properties to designing the mine planning based on the 3267 RQD data analysis of 43 drill-core within Zarshuran gold deposit in Orumieh- Dukhtar assemblage zone applying RQD-Number and RQD-Volume fractal modeling. The results of log-log plots for RQD-N model revealed four rock populations that divided by RQD thresholds 20.41, 47.86, 69.18 and 81.28. The results of log-log plots for RQD-V model release four populations divided by RQD thresholds 21.37, 43.65, 63.09, 79.43 respectively which represent very poor, poor, fair and good rocks based on Deere and Miller rock classification. In other hand the lithological units modeled based on the drill-core data to obtain the spatial distribution of Zarshuran deposit. The results of RQD-N and RQD-V fractal modeling versus lithological units modeling results revealed that Chaldagh limestone unit and Jaspiroid unit shows fair and good quality with RQD fractal value 69.18 till 81.28 and located at the center and western part of Zarshuran deposit. Therefore, in mine slop designing and planning have excellent conditions. The results of the RQD-N fractal modeling in Zarshuran deposit can usage as a practical method in similar districts.
Economic Geology
Ghodratollah Rostami Paydar
Abstract
The Zarshuran gold deposit in northwest Iran is located in historic gold and arsenic mining area in the Sanandaj-Sirjan geo-structural zone. This area is mainly composed of Precambrian rocks. The Oligo-Miocene granitoid intrusions in Pre-Cambrian formations which are the country rocks of gold mineralization ...
Read More
The Zarshuran gold deposit in northwest Iran is located in historic gold and arsenic mining area in the Sanandaj-Sirjan geo-structural zone. This area is mainly composed of Precambrian rocks. The Oligo-Miocene granitoid intrusions in Pre-Cambrian formations which are the country rocks of gold mineralization have resulted from intensive alteration, milonitization and gold mineralization. The main aim of these study is the separation of gold mineralization zones by using concentration-number (C-N) and concentration- volume(C-V) fractal techniques, which is based on 44 drill hole data and 5800 analyzed samples. Firstly, the logarithmic graph of gold was plotted for each model. Five gold mineralization zones were identified by using concentration-number model and four zones with concentration- volume model, indicate that intense of gold mineralization in wall rock, weak, medium, high and highly enriched zone, respectively. 3D geologic and fractal models show that low mineralized zones occurred in most of the ore deposits, which are often related to the Iman-Khan rock unit. In addition, based on fractal model interpretations and calculation of the overall accuracy matrices, these regions with medium, high and enriched zone have good overlaps to the Jasperoid rock unit, Chaldagh limestone, and Zarshuran shale units, respectively.
H Zamanian; Sh Rahmani; M.R Jannessary; R Zareii Sahamiieh; B Borna
Abstract
Lohneh gold and copper deposits lay in the north west of Iran, 100 kilometers north of Zanjan province. Lohneh mining area is a part of the Tarommetallogenic zone in the Alborz-Azerbaijan region. The presence of numerous minerals, slag melting of mining activities (such as cows and exploratory pits, ...
Read More
Lohneh gold and copper deposits lay in the north west of Iran, 100 kilometers north of Zanjan province. Lohneh mining area is a part of the Tarommetallogenic zone in the Alborz-Azerbaijan region. The presence of numerous minerals, slag melting of mining activities (such as cows and exploratory pits, tunnels) in the Armenian fortress (by Armenian miners) shows that the mineral reserve Lohneh have been considered by old miners. There are 9 gold bearing quartz veins .Two main quartz vein with a length of 500 meters and a width of one meter (visible on the Earth). Rock outcrops in the area consist of the Eocene-Oligocene volcanic rocks (tuffs, tuff breccia, trachyandesite) and intrusive rocks (granodiorite, quartz monzonite, monzonite). On the basis of geochemistry study, intrusive rocks is resemble the I-Type granitoids and from a magmatic stand point, the rocks of the area are calc–alkaline, and tectonically they belong to the continental margin and subduction zones. Tuff breccia rocks cut by quartz monzonite and has been altered. The major alteration of the areas consists of silicious, sericitic, and argillic alteration. The main gold minerals have occurred in tuff breccia rocks and a small amount of gold mineral in quartz monzonite. Gold mineralization in the Lohneh area is in the form of open space, vein-veinlet and hydrothermal breccia. According to chemical analysis of gold mineralized samples gold grade is in the range of at least 0.002 to 10ppm. The average gold grade is 4.35ppm. Mineralogy of Lohneh deposit has a metallic minerals (oxide, sulfide) and non-metallic (silicate and carbonate) which is composed of two phases hypogene and supergene. Metallic minerals are including gold particles (free in siliceous gangue and visible under a microscope and SEM study), silver (in the free form in siliceous and involved in galena and tetrahedrite network), pyrite, chalcopyrite, bornite, galena, sphalerite, and tetrahedrite. Non-metallic minerals or gangue consist of quartz, hydrothermal alkali feldspar (adularia), sericite, clay minerals, calcite, and small amount of barite. According to geochemical studies (table correlation of elements, graph clustering and component plot in rotated space) gold with Ag(0.78), cu(0.81), As(0.7), Pb(0.64), Zn(0.6), S(0.4), Bi(0.45), U(0.3), Mo(0.25) is a significant correlation. This correlation geochemistry is corresponded with mineralography evidence (mineral paragenesis sequence) and SEM studies. Fluid inclusion study was performed on primary, large size and rich liquid fluid inclusions on quartz mineral (concurrent with the formation of gold and sulfide minerals).Fluid inclusion data shows in the temperature range from 125 to 290 °C and salinity between 1 and 6.5 wt% NaCl and depths less than 1000 m. Fluid inclusion evidence shows cooling effect, boiling and formation of solutions with high salinity and density of the ore forming fluids in Lohneh deposits. Adularia mineral, calcite, bladed and comb quartz and hydrothermal breccia are evidence of boiling effect in the Lohneh deposits.Evidence of the presence of epithermal textures (banded, comb, blade, and hydrothermal breccia), sericitic alteration, and sulfide minerals such as galena, sphalerite, chalcopyrite, tetrahedrite, and fluid inclusions evidence (temperature, salinity, density, vapor-rich inclusions) indicates intermediate sulphidation epithermal gold deposits in Lohneh area.
R Ferdowsi; A.A Calagari; M.R Hosseinzadeh; K Siahcheshm
Abstract
Astarghan area is located in ~ 50 km of north of Tabriz, southeast of Kharvana, East-Azarbaidjn. The area is a part of Gharadagh- Arasbaran metallogenic belt. The most important units in the area is a hypabyssal prophyritic to granular granodioritic intrusive body of Oligo-Miocene and flysch- type sedimentry ...
Read More
Astarghan area is located in ~ 50 km of north of Tabriz, southeast of Kharvana, East-Azarbaidjn. The area is a part of Gharadagh- Arasbaran metallogenic belt. The most important units in the area is a hypabyssal prophyritic to granular granodioritic intrusive body of Oligo-Miocene and flysch- type sedimentry sequence of limestone, limy sandstone and marl (Paleocene-Eocene). Intrusion of the stock into the sedimentary rocks caused them to convert into a series of metasomatites and contact metamorphic rocks. Geostatistic studies on stream sediments and heavy mineral were done and include data processing, (i.e. normalization, univariate and multivariate analysis), and ultimately preparation of anomaly maps. The correlation coefficients among elements were determined. Elements that show positive correlations with gold are Cu, Hg, Pb, As, Sb, Ag, Bi and Mo. The results of preliminary regional geochemical explorations have led to discovery of two anomalous zones for gold; grade 1 and grade 2. The anomalies were verified by studies on heavy minerals in stream sediments and mineralized and altered samples taken from gold anomalous zones. The most important indentified heavy minerals include magnetite, malachite, gold, micaseous hematite, pyrite, galena, cerussite, pyrite- limonite, goethite, limonite, barite, hematite, pyrite- oxide which are affiliated with alteration and mineralzation zones. The major alterations in the area are argillic, sericitic and propylitic developed along the vein’s walls. Field and analytic studies done on samples taken from the gold anomalous zones led to identification of epithermal gold veins having over 4.5 ppm gold grade. The concordance of anomaly map with tectonic map and altered zones indicate that the faulted and fractured zones have played a crucial role in creation of gold anomalous zones. The incorporation of these data in the area led to introduction of several anomalous zones belonging to Au, Ag, Cu, As and Pb that can be used as passfinders for epithermal gold.
M Emami Jafari; M Mehrpartou; A Akbarpoor; B Shamsi
Abstract
BLEGmethod is one ofmodern methodsusedfor goldgeochemicalexplorationstudies.Themethod has helped to locate many low grade gold deposits. The significant change of the method compared to common geochemical exploration methods is to use of large volumes ofsamples regardless of their sizeandlow densityof ...
Read More
BLEGmethod is one ofmodern methodsusedfor goldgeochemicalexplorationstudies.Themethod has helped to locate many low grade gold deposits. The significant change of the method compared to common geochemical exploration methods is to use of large volumes ofsamples regardless of their sizeandlow densityof sampling.In order to evaluate the efficiency of the BLEG geochemical method with stream sediment method, 1:100000 SiahRud sheet was chosen in geological region of Azarbaijan in a district that geological map and geochemical exploration has already been carried out.The study area is 1850 km2, located in a mountainous area of northwest Iran in the Eastern-Azarbaijan province (NW of Ahar city).The rock units of the area consist mainly of the Upper Cretaceous limestone and flysch complex, Oligocene intrusive bodies and Eocene volcanic-sedimentary rocks. The Oligocene intrusive bodies are the most important igneous unit in the area.In this project, 168 BLEG samples and 103 stream sediment samples (silt samples) were prepared and studied. The range gold values in BLEG samples are from 0.1 to20 ppb, and in the stream sediment samples from 3 to459 ppb.The results ofsampling and analysis present four districts with high anomalous degrees: 1) Anigh-GharehChilar district, 2) Namnegh district, 3) Eshtobin district, and 4) Andrian or MiveRud district. Analysis ofthe stream sedimentsamplesrepresentshigh value of Cu andAu. Correlation of the elements in stream sediments taken from the Anigh-GharehChilar district represents high correlation of gold with arsenic, copper and leads elements. Copper also shows a high correlation with molybdenum, which is in accordance with mineralization of this area.
A Askari; M.H Karimpour; S.A Mazaheri; A Malekzadeh
Abstract
The Hired gold prospect area is located in the Southern Khorasan province and 140 Km south of the Birjand city. The Acidic to mafic intrusive bodies with gabbro to granite composition have intruded into the Tertiary volcano-sedimentary sequences. Based on magnetic susceptibility, the intrusives are divided ...
Read More
The Hired gold prospect area is located in the Southern Khorasan province and 140 Km south of the Birjand city. The Acidic to mafic intrusive bodies with gabbro to granite composition have intruded into the Tertiary volcano-sedimentary sequences. Based on magnetic susceptibility, the intrusives are divided into two categories: magnetite (oxidized) and ilmenite (reduced) series. The important alterations recognized on land surface and bore holes consist of: 1) quartz-tourmaline-sericite alteration, 2) carbonation alteration, 3) skarnization, and 4) propylitic alteration. Au and accompany elements mineralization (W, Sn, Bi, As, Sb, Pb, Zn, Ag) have formed as replacement, disseminate, vein-veinlet, massive, breccias, and skarn related to reduced granitic-granodioritic intrusive bodies and with different distance as compared with the bodies. Geological, mineralization, petrographical, mineralogical and alteration studies of the Hired gold deposit and comparison with the characteristics of different types of gold mineralization in the world indicate that this deposit has the most similarity with reduced intrusion-related gold systems (RIRGS). Since In this system, the most of gold reserve is accompanied with sulfide minerals and they form in roof of the reduced granitoid stocks and adjacent hornfels rocks, The IP- RS geophysical methods on reduced granitoid intrusive body and near regions was executed with the aim of recognition of hidden parts. Combination of geophysics data (IP, RS) with geological, alteration, and mineralization studies shows well development mineralization in the east of intrusive body and the country rocks. In this relation, 6 anomalous regions has been defined with Chargeability up to 30 mv/v that on the whole, they can be divided into two groups: 1) anomaly with high induced polarization and low specific resistivity resulting from presence of much metallic sulfurs as disseminate, veinlet, and massive accompanied with high sericitic alteration, 2) anomaly with high induced polarization and medium-high specific resistivity resulting from presence of much metallic sulfurs as disseminate and very high carbonation-silicic alteration.
F Mohammadi; S Alipour; M Ghazanfari
Abstract
Gold as a strategic element has a strong exploration potential in KurdistanCounty. This investigation for gold has carried out in N.W. Sanandaj- Siirjan geological zone. 351 samples has been taken from drainages and analyzed by ICP-MS in Canada for 22 elements. Based on results, anomaly map and enrichment ...
Read More
Gold as a strategic element has a strong exploration potential in KurdistanCounty. This investigation for gold has carried out in N.W. Sanandaj- Siirjan geological zone. 351 samples has been taken from drainages and analyzed by ICP-MS in Canada for 22 elements. Based on results, anomaly map and enrichment ratio for gold and related paragenetic elements have been prepared. The result indicate an enrichment factor of 1-99 times for gold and 1-3, 1-19, 1-3, 1-3, 1-6, 1-2, 1-7, and 1-4 for elements Ag, As, Pb, Zn, B, Ba, Bi and W, respectively. Data resulted to a distribution pattern for Au and other elements such as. Gold anomaly is recognize in 36 Km2 associated up to 19 times enrichment for As. Therefore As is a good indicator element for Au her and in similar environments. Tectonically gold showed a very strong relation with breccias zones and par genetic minerals.
R. Monazzami bagherzadeh; H. Mirnejad; P. Eshback; M. H. Karimpour
Abstract
Listvenites or ophiocarbonates are considered important for exploration of precious and base metlas particularly Au, Ag, Cu, As and Hg. These rocks, which crop-out dominantly in ophiolite-mélange zones and in the vicinity of main faults and shear zones, have formed as the result of hydrous ...
Read More
Listvenites or ophiocarbonates are considered important for exploration of precious and base metlas particularly Au, Ag, Cu, As and Hg. These rocks, which crop-out dominantly in ophiolite-mélange zones and in the vicinity of main faults and shear zones, have formed as the result of hydrous and carbonic alteration of ultramafic rocks. Listvenites occur extensively in eastern Iran. Based on petrography, Hangaran listvenites are grouped into three major types: 1. Carbonatic listvenite (type I), 2. Silicic listvenite (type II), and 3. Sulfie-bearing silicic listvenite with brecciated texture (type III). Gold contents of listvenites is generally low and the highest concentration (290 ppb) has been found in type III. Studies of mineral concentrates from stream sediments reveal the presence of gold, pyrite, chalcopyrite, cinnabar and native copper. Gold grains reach to a maximum sizes of 80 microns, and they are often associated with pyrite. Electron microprobe analyses on several sulfides and carbonates in Hangaran listvenites show that sulfide minerals are mainly pyrite, marcasite, bravoite and to a lesser amount chalcopyrite, and that many pyrite grains have been altered to marcasite. Important carbonated minerals are magnesite and dolomite. The presence of obiquitous bravoite zonation that results from alternations in Ni content indicates periodic changes in the physicochemical conditions of the hyrdorthemal solution. Petrographic studies and paragenetic sequence of minerals show that magnesite and dolomite formed prior to the mineralization stage, which was then followed by the formation of sulfides (mainly pyrite). Studies on the oxygen and carbone isotopes in 3 dolomite samples (δ18OSMOW = 9.353- 9.982 ‰, δ13CPDB =1.57- 1.67 ‰ ) show that oxygen and carbone can originate from oceanic waters, and that dolomite has formed due to the circulation of this water in ultramafic rocks and their subsequent alteration. Considering the variation in marcasite-pyrite paris from Hangaran silicic listvenite (δ34SCDT value 5.7-7.9 ‰ ), it seems that sulfur has originated from granitic rocks in south of the study area. Taking into accout the extentive outcrops of serpentinized ultramafic rocks and granite in the region can considered the source of Au, Ag and base elements such as Cu, Pb, Zn, Hg, As, Sb in related to granite masses, and Cr, Ni, Ti and Fe in related to serpentinized ultramafic rocks. Fluid inclusion studies on mineralized quartz in Hangaran listvenites show that the hydrothermal fluid affecting the host rocks was low salinity and had a maximum temperature of 280ºC.
M. Abdollahy; S. M. J. Koleini; A. Ghaffari
Abstract
Cyanidation process is one of the most important and widespread hydrometallurgical technologies used in the extraction of gold and silver from ores and concentrates. Some of the most effective parameters on cyanide leaching are sodium cyanide concentration, dissolved oxygen, solid percent, pH, particle ...
Read More
Cyanidation process is one of the most important and widespread hydrometallurgical technologies used in the extraction of gold and silver from ores and concentrates. Some of the most effective parameters on cyanide leaching are sodium cyanide concentration, dissolved oxygen, solid percent, pH, particle size, retention time and agitation speed. In this article the effect of these parameters on the recovery of gold, silver and mercury from Pouya Zarkan Aghdareh ore has been studied to determine the optimum conditions using Taguchi exprimental design method. The experiments at the screening step based on L16 orthogonal array indicated that the effective parameters on gold, silver and mercury recovery such as sodium cyanide, pH, solid percent in pulp, d80 and retention time were obtained equal to 900 g/t ore, 10, 42%, 53 μm and 30 h, respectively. The experiments at the optimization step based on L18 orthogonal array indicated that d80 on gold recovery and retention time on silver and mercury recovery were the most effective parameters. Finally the optimum conditions for gold, silver and mercury recovery were obtained for parameters such as sodium cyanide, pH, solid percent in pulp, d80 and retention time equal to 1000 g/t ore, 10.3, 46%, 37 μm and 40 h, respectively. At this conditions gold, silver and mercury recovery were equal to 91.42±1.02, 54.31±1.24 and 19.50±0.66 percent, respectively.
E. Ashrafpour; K. M. Ansdell; S. Alirezaei
Abstract
Arghash gold district includes five gold-bearing vein systems, (Au-ItoAu-V) and one antimony-rich vein hosted by intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Pyrite is the main sulfide mineral consisting of four generations (Py-ItoPy-IV). Py-I toIII are intimately ...
Read More
Arghash gold district includes five gold-bearing vein systems, (Au-ItoAu-V) and one antimony-rich vein hosted by intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Pyrite is the main sulfide mineral consisting of four generations (Py-ItoPy-IV). Py-I toIII are intimately associated with gold; however, Py-IV is barren. The δ34S values of pyrites in conventional bulk analyses fall into two groups, one highly enriched in 34S (δ34S= +9.3 to +21.8‰), and the other less enriched to slightly depleted in 34S (δ34S= +5.1 to -4.3‰). In-situ laser probe experiments were carried out to characterize various generations of pyrite. The results indicate a relatively narrow range for Py-I to Py-III (δ34S= -5.8 to +0.1‰) consistent with a magmatic source for sulfur. Py-IV is highly enriched (δ34S= +8.9 to +23.7‰), implying contributions of sulfur from sources enriched in 34S, like evaporites. The high δ34S values in the enriched group can be attributed to a significant occurrence of Py-IV in this group.
The δ34S values of two stibnites from Sb ore (-18.8 and -14.4‰) suggest a different sulfur, and possibly metal source, and/or radical changes in the physicochemical conditions of the fluid during deposition of stibnite. Metasedimentary basement rocks could contribute sulfur and metal to the circulating fluids. δ13CPDB values of vein calcites are near 1 per mil suggesting a sedimentary source for carbon. Carbonate units and interlayers in the area are a suitable source for CO2 in the ore fluids. The stable isotope data suggest that hydrothermal fluids experienced a complex history of water/rock interaction and that ore components, were derived, at least partly, from country rocks.
E. Ashrafpour; S. Alirezaei; K.M. Ansdell
Abstract
Arghash gold district is located in the eastern Sabzevar zone. The basement of this zone consists of Precambrian metamorphosed rocks and Paleozoic-Mesozoic epicontinental sediments. The basement is covered by Upper Cretaceous ophiolitic mélange and Tertiary magmatic and sedimentary rocks. Arghash ...
Read More
Arghash gold district is located in the eastern Sabzevar zone. The basement of this zone consists of Precambrian metamorphosed rocks and Paleozoic-Mesozoic epicontinental sediments. The basement is covered by Upper Cretaceous ophiolitic mélange and Tertiary magmatic and sedimentary rocks. Arghash district includes five gold-bearing vein systems, Au-I–Au-V, and one Sb vein, occurring in Tertiary intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Intensive alteration, dominated by clay minerals, is confined to 1 to 5 m from the veins. The intensive argillic alteration is bordered by irregular zones of moderate to weak argillic and propylitic alterations.
Mineralization is mostly confined to veins. Pyrite is the main sulfide mineral and includes four generations: 1) disseminated euhedral to anhedral, fine- to coarse-grained pyrite (Py-I), locally associated with minor chalcopyrite, marcasite, tetrahedrite-tennantite, and arsenopyrite; native gold grains occur in quartz associated with the pyrite; 2) framboidal pyrite (Py-II) which contains up to 960 ppm Au; 3) arsenian pyrite overgrowths (Py-III) which contain up to 1980 ppm Au; and 4) fracture-filling, anhedral, barren, late stage pyrite (Py-IV). Gold occurs as nanoparticles as well as unstable solid solutions in the framboidal and arsenian pyrite.
Homogenization temperature (Th) and salinity were measured on fluid inclusions in several quartz and calcite samples. Th varies from 186º to 357ºC, and 169º to 313ºC, and salinity from 0.2 to 5.3 and 0.7 to 1.9 wt. percent NaCl equiv. for quartz and calcite, respectively. The low salinity character of the ore forming fluid is consistent with the ore mineralogy and metal contents. The variation in salinity and Th could be explained by a combination of boiling and mixing (dilution) of a hotter and more saline fluid with a cooler and less saline fluid. These processes led to the deposition of gold in the veins. The ore mineralogy, textures, alteration, homogenization temperatures, and salinities, are typical of low-sulfidation epithermal precious metal deposits.
S. Ebrahimi; Y. Pan; S. Alirezaei; M. Mehrpartou
Abstract
The Sharafabad auriferous epithermal vein system is located in the Alborz-Azarbaijan magmatic assemblage in northwestern Iran. The veins are hosted by Eocene andesitic volcanic and pyroclastic rocks and tuffs. Wall rock alteration includes an inner silicic zone often bordered by argillic and propylitic ...
Read More
The Sharafabad auriferous epithermal vein system is located in the Alborz-Azarbaijan magmatic assemblage in northwestern Iran. The veins are hosted by Eocene andesitic volcanic and pyroclastic rocks and tuffs. Wall rock alteration includes an inner silicic zone often bordered by argillic and propylitic zones. Mineralization is mainly restricted to silica and silica-carbonate veins and veinlets in faults and fault zones. A total of 18 ore-bearing veins have been identified. The veins vary from 10 -1000 meters in length and 0.5-10 meters in width, respectively. Pyrite is the main sulfide, commonly associated with subordinate chalcopyrite, sphalerite, and galena. Gold occurs as scattered microscopic grains in quartz and pyrite, and along the grain boundaries of the sphalerite, galena and chalcopyrite. Silica occurs as gray quartz, white quartz, clear quartz, opal, chalcedony, and minor amethyst. On the basis of crosscutting relationships and mineral paragenesis, four stages can be distinguished: (I) pre-mineralization, (II) mineralization, (III) post-mineralization and (IV) supergene. The gold and the base metals sulfides occurred in the mineralization stage. Fluid inclusion data have been obtained from the ore-stage gray quartz and sphalerite, carbonates, and the late clear quartz and amethyst. The fluid inclusions from the gray quartz indicate homogenization temperatures of 170-270 ºC and salinities of 1 to 8.7 wt% NaCl equiv. The fluid inclusions in the sphalerite indicated homogenization temperatures of 215-265 ºC, and salinities of 10.8-15.3 wt% NaCl equiv. The carbonates formed at lower temperatures, between 160-250 ºC, from fluids of low salinities, at 1.5-3.8 wt% NaCl equiv. Amethyst from final stages of vein formation, not associated with sulfides and gold was deposited at 173-203 ºC from fluids containing 3.5 to 9.5 wt% NaCl equiv. The coexistence of vapor-dominant and liquid-dominant inclusions in quartz and sphalerite suggests that boiling occurred during the evolution of the ore fluids. The occurrence of boiling is supported by hydrothermal breccias, bladed calcite, and adularia. Fluid inclusion data suggest that ore was deposited at an average depth of about 400 m below the paleosurface. Considering the intermediate argillic alteration, association of gold with base metal sulfides, and the moderate salinities, the Sharafabad district can be classified as an intermediate-sulfidation epithermal system.
A. R. Sayadi; M. Yavari; N. Solgi
Abstract
Exploration projects need considerable investments. These projects are associated with high techno-economical risks. Therefore, Evaluation of exploration potential is necessary. It is determined in primary stages of exploration whether the deposit reserve is not economic or the ...
Read More
Exploration projects need considerable investments. These projects are associated with high techno-economical risks. Therefore, Evaluation of exploration potential is necessary. It is determined in primary stages of exploration whether the deposit reserve is not economic or the grade is less than normal grade, and it may be decided to stop the project. The minimum acceptable target reserve is known as a criterion for determining the economic potential of deposit regarding to techno-economical environment of project. In this research a new model is proposed for determining minimum acceptable target reserves in gold projects. This model is verified through the economic filed data from Zarshpran gold mine. The graph of grade versus tonnage and internal rate of return versus tonnage are demon stared through Excel software. The results of this research could be used as powerful decision making tools in gold exploration projects.