تعيين دگرساني‌هاي هيدروترمال مس پورفيري با استفاده از روشهاي آناليز چند متغيره بر روي داده‌هاي ليتوژئوشيميايي در منطقه حراران، استان كرمان

Determination of Cu porphyry hydrothermal alterations using multivariate analysis methods on lithogeochemical data in Hararan area, Kerman province

روش­های آماری چند متغیره كاربردهای زیادی در علوم وابسته به زمین شناسی خصوصا ژئوشیمی پیدا كرده­اند. در این مطالعه از آنها به عنوان كاربردی جدید برای تشخیص دگرسانی­های نوع آرژیلیك، پتاسیك و پروپلیتیك (دگرسانی­های عمده موجود در كانسار­های مس پرفیری) استفاده شده است. منطقه حراران واقع شده است. برای تعیین مناطق دگرسان شده از 607 نمونه لیتوژئوشیمیایی استفاده شده است؛ این نمونه­ها از منطقه حراران واقع در در نقشه 1:100000 شهرستان بافت استان كرمان  اخذ شده­اند كه در این منطقه كانی­زایی مس پورفیری رخ داده است. نمونه­ها برای 45 عنصر به روش ICP-MS و در آزمایشگاه  Amdelاسترالیا آنالیز شده اند كه از بین آنها عناصر Ca, Na, Al, Fe, S, K, Rb, Mgبرای انجام این پژوهش انتخاب شدند.  نتایج آنالیز خوشه­ای بر روی متغیر­ها و بر روی نمونه­ها دو خوشه نشان دادند: خوشه اول شامل عناصر K, Rb, S, كه منطبق بر دگرسانی نوع پتاسیك و آرژیلیك و خوشه دوم نیز شامل عناصر Mg, Ca, Na, Al, Fe است كه دگرسانی نوع پروپلیتیك را نشان می­دهند. نتایج آنالیز فاكتوری نیز نتایج فوق را تایید كردند و حتی نقشه فاكتور اول در قسمت­های جنوبی منطقه، نواحی كوچكی از آلتراسیون آرژیلیك و پتاسیك را نیز مشخص كرد كه این مناطق توسط روش آنالیز خوشه­ای بر روی نمونه­ها مشخص نشده بودند.

Summary In geological sciences, especially geochemistry, multivariate statistical methods have many applications. So that, they were employed as a new application for recognition main alterations in Cu-Mo porphyry system such as argillic, potassic, and propylitic alterations. For determination of alteration areas, results of 607 lithogeochemical samples were utilized in Hararan area, which appears to possess the potentiality for porphyry mineralization and locates in Baft sheet (1:100,000 series) in the southeast of Iran. 607 rock samples were analyzed by ICP-MS in Amdel laboratory for 45 elements. However, it used just the results of Ca, Na, Al, Fe, S, K, Rb, Mg elements for this paper.  Results of hierarchical cluster and k- means Cluster methods showed two different clusters: K, Rb, S elements and Mg, Ca, Na, Al, Fe elements have been in cluster 1 and cluster 2, respectively. Cluster1 and cluster2 introduced as potassic and argillic alterations and propylitic alteration, respectively. The results of factor analysis not only confirmed the above results but also the first factor map depicted small areas of argillic and potassic alterations in the southern parts of the region, so that these areas did not identify by k-means cluster method.   Introduction Hydrothermal Alteration plays a key role in types of mineralization. For recognition of alteration zones, there are common techniques such as mineralogical, lithological studies and field surveys. Researchers used different methods for identifying alteration zones. Therefore, in this study, it was utilized multivariate analysis techniques as a new application for mentioned objective.   Methodology and Approaches In regional geochemistry an advantage would be that instead of presenting maps for 40–50 (or more) elements only maps of 4–6 factors may have to be presented, containing a high percentage of the information of the single element maps. It is even more informative if factor analysis can be used to reveal unrecognized multivariate structures in the data that may be indicative of certain geochemical processes, or, in exploration geochemistry, of hidden mineral deposits. Cluster analysis is used to delineate the relationships between elements and shows which elements tend to have similar variations in concentrations.   Results and Conclusions In this study, 607 lithogeochemical samples were analyzed for 44 elements. But Ca, Na, Al, Fe, S, K, Rb, Mg were selected to recognize alteration zones in Hararan area. Before performing multivariate analysis, the preprocessing of geochemical data was performed including the replacement of censored and outlier data. The results of factor and cluster analysis showed that Fe, Ca, Al, Na, Mg elements and K, Rb, S elements represented Propylitic and argilic alteration, respectively.