كاني سازي مگنتيت توده اي طلادار در كاشمر (مطالعات دگرساني، كاني سازي، ژئوشيمي و سيالات درگير) و تكتونوماگماتيسم شمال شرق ايران

Aubearing magnetite mineralizaion in Kashmar (alteration, mineralization, geochemistry, geochemistry and fluid inclusions); and Tectonomagmatism of northeast of Iran

منطقه اكتشافي در 30 كيلومتري شمال شرق كاشمر، در بخش مركزي كمربند آتشفشاني و نفوذي خواف كاشمر بردسكن واقع شده است. زمين شناسي منطقه شامل سنگهاي آتشفشاني و نفوذي نيمه عميق و عميق مافيك تا اسيدي كالك‌آلكالن با توانايي بالا و شوشونيتي به سن پالئوسن ائوسن مياني است. توده هاي گرانيتوئيدي با پذيرفتاري مغناطيسي از 2 تا (SI)510 × 1654 جزو دسته مگنتيتي ايلمنيتي هستند. دگرساني و كاني سازي به دو صورت: 1) دگرساني بيضوي خطي شديد تا متوسط آرژيليك سيليسي و سرسيتي شدن و دگرساني متوسط پروپليتيك همراه بارگه هاي كالكوپيريت كوارتز ± پيريت در مناطق بهاريه، اوچ پلنگ و سرسفيدال، و 2) دگرساني متوسط هماتيتي كربناتي كلريتي سيليسي همراه با رگه هاي غني از اسپكيولاريت، كوارتز – گالن و باريت عقيم به‌همراه برش گرمابي در كمرمرد است. رگه ها بي هنجاري عناصر طلا، مس، سرب و روي دارند. بيشترين غني شدگي طلا (تا 15 پي پي ام) به‌همراه مس، سرب و روي (هر كدام تا >1 درصد) در برش گرمابي و رگه هاي غني از اسپكيولاريت رخ‌داده است. بر اساس بررسي سيالات درگير، سيستم به‌صورت H2ONaClCaCl2، دماها متوسط تا نسبتاً زياد و بين 245 تا 530 درجه سانتي گراد و شوريها نسبتاً كم تا متوسط (بين 14 تا 6/17 (wt% NaCl)) است. دماها و شوريهاي بيشينه و كمينه به‌ترتيب مربوط به سيالات درگير برش گرمابي و رگه هاي كوارتز گالن است. هم‌زيستي بين سيالات درگير دوفازي غني از مايع و بخار و سيالات تك فاز گازي كم در رگه ها، برشي‌شدن سنگ و مشاهده سيالات درگير نوع CO2‌دار اندك در رگه هاي قله كمرمرد و نبود كوارتز حفره دار در كلاهكهاي سيليسي منطقه، نشان‌دهنده شرايط نزديك به جوشش است. فراواني كانيهاي اسپكيولاريت و باريت و مقدار كم كانيهاي سولفيدي نشان دهنده شرايط اكسيدان محلول و تأثير كمپلكس هاي كلريدي CO2‌دار در حمل، دخالت نداشتن آبهاي متئوريك و ته‌نشست عناصر فلزي محلول گرمابي با كاهش تدريجي دما است. شواهد مختلف بيانگر سطحي ترين و بخشهاي با عمق متوسط از يك سيستم كاني سازي مگنتيت طلا دار نوع IOCG دور از كمان در كاشمر است.

Introduction The study area is located in the central part of the Khaf Kashmar Bardaskan volcanoplotunic belt (briefly KKBB). Several IOCG deposits such as Tanourjeh Aubearing magnetite deposit and KuheZar Speculariterich Au deposit have been explored in KKBB. Geology, alteration, mineralization, geochemistry and fluid inclusion results in Kashmar suggest the IOCG type Aubearing magnetite mineralization. These IOCG deposits at KKBB form at an active continental arc related to SSZtype Sabzevar oceanic subduction. Materials and methods Use of Landsat 7+, IRS and Aster satellites. Petrography and alteration Studies in 150 thin sections of volcanic and intrusive rocks. Sampling of orebearing quartz vein and mineralography. Preparation of 28 geochemistry samples by the chip composite method of orebearing quartz vein and analyzing them in the ACME laboratory by Aqua Regia 1DX1. Fluid inclusions studies of 14 samples of quartz and barite related to the ore minerals of orebearing quartz vein by THM600 stage of Linkam company. Results Magmatic events in Kashmar occur at PaleoceneEocene and include: (1) old mafic intermediate volcanoplutonic series; (2) felsic volcanic and granitoids; and (3) parallel swarm dykes which are youngest (Almasi et al., 2016). Geochemically, Kashmar rocks are metaluminous to highly peraluminous and Tholeitic to calcalkaline and shoshonitic in composition (Almasi et al., 2016). The field characteristics, together with isotope and geochemical analyses show that all rock types are essentially comagmatic and postcollisional Itype (Almasi et al., 2016). Alteration of Kashmar is described in two ways: (1) intense ellipsoidallinear ArgillicSillicification and low sericitic with Silica caps and with medium widespread and propylitic alterations in triple regions, next to Dorouneh fault; and (2) Medium HematiteCarbonateChloriteSilicification alterations in Kamarmard heights. In parts of near the Doruneh fault, sometimes fractures of rocks are filled with tourmaline (Dumortierite type) and iron oxides. Kashmar surface mineralization is described in the orebearing quartz veins. Principal mineralization textures are layered, comb and Brecciation. The most important types of veins are those containing Chalcopyrite Quartz veins, Speculariterich veins – QuartzGalena veins accompany with hydrothermal Breccias. Barren barite veins also exist in the region. The Chalcopyrite Quartz veins occur on the main fracture zone and next to the Argillic alterations and silica cap in three regions (Bahariyeh, Uch Palang and Sarsefidal). Hydrothermal Breccias, Spicularite rich veins, Quartz Galena and barite veins occurred within Hematite CarbonateChloriteSilicification alterations in the Kamarmard area. Geochemistry of veins indicates anomalies of gold, copper, lead and zinc in them. Most enrichments of gold are accompanied with copper, lead and zinc and they occurs in hydrothermal Breccias and then specularite rich veins. Gold values up to about 15 ppm and Cu, Pb and Zn each to > 1%. Temperature – salinity studies of fluid inclusions of orebearing Quartz veins in Kashmar show the fluid temperature and salinity values in all veins are close together. Temperatures are moderate to relatively high and between 245° C and 530 ° C and salinities are relatively low to moderate and between 14 to 18 (wt% NaCl). Maximum and minimum of temperatures and salinities are related to fluid inclusions of hydrothermal Breccias and QuartzGalena vein. Coexistence between twophase liquidvapor rich fluids and singlephase gas fluids in the veins indicate that conditions were close to boiling, and maybe a little boiling occurred, which strengthened with brecciaing of rock and view rare CO2bearing fluid inclusion in veins on the Kamarmard peak. Nonexistence of vuggy Quartz in silica caps in the region shows this issue. The frequency of oxide minerals (Specularite, Barite), H2ONaClCaCl2 system, and the low amounts of sulfide minerals in Kashmar, all represent the oxidized conditions of hydrothermal fluid and the impact of CO2bearing chloride complex in transport, noninterference of meteoric waters and precipitation of metallic elements with reducing of temperature. Discussion Most important IOCG deposits of south America (Candelaria, Mantoverde and Raul Condstable) have Aubearing massive magnetite bodies accompanied with Potassium (actinolite, biotite and Kfeldspar) alterations with high temperatures (500700 O C) and salinities ( >40%wt NaCl) at deepest parts (Sillitoe, 2003). At the upper levels, there are magnetite changes to hematite (Specular) and the possibility of coarse calcite (± silver mineralisation). Hematite zone may display hydrothermal/tectonic brecciation. The hematiterich veins tend to contain sericite and/or chlorite, with or without Kfeldspar or albite, and to possess alteration haloes characterized by these same minerals. Both the magnetite and specular hematiterich IOCG veins contain chalcopyrite and generally subordinate Pyrite (Fuller et al., 1965). References Almasi, A., Karimpour, M.H., Ebrahimi Nasrabadi, Kh., Rahimi, B. and KlÖtzli, U, 2016. Geology and geochemistry of subvolcanic and plutonic bodies of Kashmar (North of Lut Block). Iranian Journal of Crystallography and Mineralogy, 24 (3): 539556. (in Persian) Fuller, R.C., Corvala´n, J., Klohn, C., Klohn, E. and Levi, B., 1965. Geologı´a y yacimientos metalı´feros de Chile. Instituto de Investigaciones Geolo´ gicas, Santiago, 305 pp. Sillitoe, R.H., 2003. Iron oxidecoppergold deposits: An Andean view. Mineralium Deposita, 38(7): 787–812.