کانی‌شناسی و ژئوشیمی بخش سولفیدی معدن سرب و روی طرز، شمال استان کرمان، مورد مطالعاتی از کانسارهای رسوبی با سنگ میزبان کربناته

کانسار سرب و روی طرز یکی از معادن فعال زیرزمینی در ناحیۀ راورکوهبنان است که در شمال استان کرمان قرار دارد. کانه‌زایی در این معدن به‌طور مجزا در دو بخش کربناته و سولفیدی در واحدهای کربناتۀ تریاس میانی (سازند شتری) مشاهده می‌شود. بررسی‌های صحرایی نشان می‌دهند کانسارسازی در راستای گسل‌ها به‌شکل رگه‌ای و رگچه‌ای و به مقدار کمتر به‌شکل توده‌ای شکل گرفته است. مهم‌ترین کانی‌های سولفیدی اولیه در معدن سرب و روی طرز شامل گالن، اسفالریت، پیریت و کالکوپیریت هستند. کانی‌های ثانویۀ مرتبط با کانسارهای سرب و روی ازجمله اسمیت زونیت، همی‌مورفیت، سروزیت و آنگلزیت نیز در برخی نمونه‌ها شناسایی شدند. در نمونه‌های مطالعه‌شده، متوسط غلظت سرب و روی به‌ترتیب 19 و 24 درصد بود. عناصر دیگر مانند cd، ag، s، sb، te، se، as و cu نیز در نمونه‌های بررسی‌شده غنی‌شدگی نشان دادند. ارزیابی نتایج با روش‌های آماری چندمتغیره، ارتباط احتمالی بین فازهای کانی‌شناسی و نتایج ژئوشیمیایی را مشخصکرد؛ برای نمونه، همبستگی عناصر pb، ag، tl و sb ممکن است با کانه‌زایی گالن مرتبط باشد و یا ارتباط ژئوشیمیایی عناصر as، bi، cu، p، fe، co و s ممکن است از کانه‌زایی پیریت و کالکوپیریت متاثر باشد. روابط آماری نشان دادند عنصر zn تنها همبستگی ژئوشیمیایی ضعیفی با عناصر se، u و mo دارد. همبستگی زیاد ca و mg نیز از کانی‌شناسی سنگ میزبان متاثر است که عمدتاً از کانی درشت‌بلور (در حاشیۀ رگه‌های کانه‌زا) و دولومیت ریزبلور (دور از رگه‌های کانه‌زا) تشکیل شده است.

Mineralogy and geochemistry of sulfide zone of Tarz PbZn mine, North of Kerman province: A case study of carbonatehosted sedimentary ore deposits

Abstract The Tarz PbZn deposit is one of the underground active mines in the RavarKuhbanan area, located in the North of Kerman province. In this mine, mineralization was observed in two distinct sulfide and carbonate divisions within the dolomiticlimestone host rock units of the Middle Triassic succession (Shotori Formation). Field observations show that mineralization occurred mainly along the faults as veins or veinlets and in lesser extent as massive textures. Galena, sphalerite, pyrite and chalcopyrite are the most important primary sulfide minerals in the Tarz PbZn deposit. Secondary minerals associated with the PbZn deposits such as smithsonite, hemimorphite, cerussite and anglesite were also identified in some of the investigated samples. The average concentrations of Pb and Zn were 19 and 24% in the studied samples, respectively. Other elements such as Cd, Ag, S, Sb, Te, Se, As and Cu also showed significant enrichment in the investigated samples. Evaluation of the obtained results using multivariate statistical methods can reveal the possible relationships between mineralogical phases and geochemical analysis. For example, the correlation between Pb, Ag, Tl and Sb can be related with the galena mineralization or the geochemical relationship between As, Bi, Cu, P, Fe, Co, and S is related with the pyrite and chalcopyrite mineralization. Statistical relationships also showed that Zn has only a weak geochemical association with Se, U and Mo. The strong correlation of Ca and Mg is also due to the hostrock mineralogy, which is mainly composed of course and fine crystal dolomites at the margin and far distances of ore veins, respectively. Keywords: Mineralogy, Geochemistry, Tarz PbZn deposit, Kuhbanan, North of Kerman   Introduction Tarz PbZn deposit is located at 30 km east of Kuhbanan and 5 km southwest of the Tarz village in the North of Kerman Province. From geological point of view, this mine is located on the southeastern margin of the Bahabad PbZn belt, which is a part of TabasPoshteeBadam metallic belt of the Central Iran (Alavi 1991; Rajabi et al. 2013). In this area, there are a large number of PbZn deposits that mostly occurs in the Triassic dolomitelimestone beds of the Shotori Formation. Major faults such as Kuhbanan and Behabad with NWSE direction have been very effective role in the development of geology and mineralogy history of this region. However, The dominant trend of the faults in Tarz PbZn deposit is about N40E, but field observations showed various faults and fractures in different directions, which demonstrate the active tectonic of this area. For example, one of the major mineralization parts of the mine was in a shearing zone produced by four major faults with NWSE direction. Some authors such as Amiri et al. (2009) believe that based on the position of mineralized sections in the carbonate host rocks the Tarz PbZn mine is classified as the Mississippi Valley Type (MVT) deposits. In the Tarz mine, mineralization is observed in two distinct sulfide and carbonate sections, which are located in the north and south of the mine, respectively. This study emphases on the texture, mineralogy and geochemistry of sulfide section of the Tarz PbZn deposits in order to determine the elemental dispersion, and reconstruction of depositional history of Pb and Zn minerals.   Materials & Methods Fifty rock samples were collected from mineral veins and hostedrock for mineralogical studies of sulfide section of the Tarz PbZn mine. Ore mineralogy studies were done on the 30 polishedthin section and five polishedblocks by reflecting and polarizing microscope (OLYMPUS BH2 model) at the Geology Department of Shahid Bahonar University of Kerman. Also, eight samples were selected for further mineralogical studies by Xray diffraction (XRD) method in the Zarazma Laboratory, Tehran, Iran. After mineralogical studies, 10 samples were selected for major and trace elements analysis by the ICPMS method in the Zarazma Laboratory. Geochemical data were used to (1) calculate enrichment factor; (2) identification of enriched elements; and (3) geochemical correlations of target elements. The spider diagrams of major and trace elements were plotted in order to determine their changes from ore veins to the surrounding hosted rocks. For drawing of spider diagrams, the data were normalized against the standard limestone.   Discussion of Results & Conclusions Mineralogy Mineralogical studies using ore microscopy and XRD showed that both primary and secondary minerals are present in the sulfide section of the Tarz deposit. The most important primary minerals were galena (about 60%), sphalerite (less than 40%), pyrite and chalcopyrite. These minerals were often found in the mineralized sections in the northern part of the mine, where mineralization occurs mainly as veins and veinlets, breccia and in lesser extent as porefilling structures. The secondary minerals including smithsonite, hemimorphite, cerussite, anglesite and iron oxides also were identified in different parts of the mine. In addition to the mentioned minerals, dolomite and calcite were also observed as the main minerals of the hostedrocks. The identified dolomites minerals can be classified into two groups including finecrystalline and sudhedral, coarse crystalline or saddle dolomite. It seems that finecrystalline dolomites have formed as primary minerals during the early time of diagenesis, while the coarsecrystalline dolomites have formed by hydrothermal fluids. Calcite in the hosted rocks was mainly in the form of microcrystalline or micrite type and it seems that this mineral is not affected by the PbZn mineralization process.   Structure and texture The structures and textures of mineralization in the Tarz mine, were as veins and veinlets, massive, breccia, porefilling and replacement types. These structures are mainly related to the active fault system of the region. Galena, sphalerite, pyrite and dolomite were the most important primary minerals in most of mineralized textures, however, secondary minerals such as smithsonite, hemimorphite and cerussite were also observe in porefilling and replacement textures.   Geochemistry According to the results obtained from normalized enrichment factor Pb, Cd, Zn, Ag, S, Sb, Te, Se, As and Cu have moderate to high enrichments in the investigated samples, respectively. Also, U, Tl, Bi, Mo, Co and Cr showed low enrichments in some samples. The geochemical relationships between enriched elements was well compatible with the mineralogical results. For example, identified sulfide minerals (galena, sphalerite, pyrite and chalcopyrite) have a great potential for replacing of several of enriched elements in their crystalline structures as impurities. The geochemical associations of most of the target elements in sulfide minerals can be considered as possible mechanisms for enrichment of these elements in the investigated samples. These geochemical association can be revealed using multivariate statistical methods. For examples, the following groups of geochemical associations were observed in the investigated samples: 1     The correlation between Pb, Ag, Tl and Sb, which can be related with the galena mineralization; 2     The correlation between P, Cu, Bi, As elements with Fe, Co and S can be related with the pyrite and chalcopyrite mineralization; 3     The strong correlation between Ca and Mg is due to the mineralogy of the hostrock minerals; 4     Zinc only showed a weak correlation with Mo, U and Se, which may be due to the alteration and weathering of its primary sulfide minerals mainly into the secondary carbonate minerals; The spider diagrams of major elements showed that except iron, other elements have the same values with standard limestone. Ore forming processes, especially the presence of sulfide minerals such as pyrite, chalcopyrite and even sphalerite are responsible for iron enrichment in the investigated samples. Contrasting to the most of major elements, trace elements, especially Pb, Cd, Zn, Ag, S, Sb, Te and Se, As and Cu, showed strong deviation from their values in the standard limestone. Concentration of these elements were decreased by increasing distance from ore veins to the host rock.   Possible mineralization model The PbZn mineralization in the Tarz mine as well as other ore deposits in the RavarBahbad region is often as veins and veinlets. A variety of lithological and structural factors control PbZn mineralization in this region. According to Leach et al. (2005) diagenesis and tectonic processes have a fundamental role in the formation of MVT type PbZn deposits. Field observation demonstrate that active tectonic and formation of a complex fault system have more important role than other factors in the formation of Tarz PbZn deposit. Comparison of the obtained mineralogical and geochemical data in this study with the previous researches revealed that the PbZn mineralization in Tarz area is more similar to the MVT type. Nevertheless, to determine the source of orebearing fluids and to draw up a comprehensive mineralization model, isotopic and structural data are required.