بررسي كاني‌ شناسي و ژئو فيزيك معدن سرب و روي منطقه مرجان‌ آباد منجيل

Mineralogical and geophysical study of the lead and zinc mine in Marjan-Abad region, Manjil

معدن سرب و روي مرجان‌آباد تحت تأثير زون‌هاي گسله و تكتونيكي بوده وكاني‌سازي درامتداد زون‌هاي گسله قرار دارد. سنگ‌هاي منطقه بيشتر از نوع ريوليت، داسيت و به مقدار كم آندزيت و بازالت و از نوع آلكالن تا كالكو آلكالن هستند. از جمله بافت‌هاي موجود در اين كانسار، بافت رگه‌اي است. بي‌هنجاري‌هاي مغناطيسي و گراني در اين منطقه مشاهده شده است كه ناشي از آثار تكتونيكي محيط و كانه‌زايي در بين رگه‌ها هستند. اغلب سنگ‌هاي اين منطقه در محدودۀ سنگ‌هاي اسيدي قرار گرفته‌اند. با استفاده از داده‌ها و مطالعات صحرايي ژئوفيزيكي چهار منطقۀ اميدبخش معدني مشخص شده‌اند كه با يكديگر هم‌پوشاني دارند. هم‌پوشاني نتايج بي‌هنجاري‌هاي مغناطيسي وگراني در اين چهار منطقه مي‌تواند مهم باشد، زيرا هرجا دو بي‌هنجاري مغناطيسي وگراني هم‌پوشاني داشته باشند، احتمال پيدايش كانسار بيشتر است. در مجموع در تحليل اطلاعات ژئوفيزيك هوابرد اين چهار منطقه نتايج مثبتي ارائه شده كه عبارت‌اند از: دست‌يابي به الگوي گسل‌هاي منطقه و معرفي مناطق اميدبخش معدني بر اساس بي‌هنجاري‌ها؛ زيرا دراين مناطق با توده‌هاي آذرين ساب ولكانيكي رو‌به‌رو هستيم كه براثر فعاليت‌هاي پساماگمايي سنوزوئيك تحت تأثير محلول‌هاي هيدروترمال قرارگرفته و ضمن پيدايش هاله‌هاي دگرساني، موجب شكل‌گيري كانه‌ها در امتداد رگه‌ها شده است. تيپ اين كانسار به تيپ كانسار درۀ مي‌سي‌سي‌پي شبيه است.

The Marjan Abad zinc and lead mine has been affected by fault and tectonic zones and the mineralization are mainly located along the fault zones. Rocks of the area are mainly rhyolite, dacite with small amounts of andesite. Basalt consists of kind of alkaline to calc-alkaline. streak texture which is the main texture of this deposit. Gravity and magnetic anomalies are observed in this area that are the result of effects of tectonic structures and mineralization in between streaks. Rocks in the region are often acidic. As it is recognized, using geophysical data and field studies for mineral prospecting can be important, as magnetic and gravity anomalies overlap in four regions. The deposits usually have overlapping magnetic and gravity anomalies. The mineral deposits, found by the geophysical anomalies, are due to post-magmatic activated in Cenozoic, as the area includes sub-volcanic igneous masses. The area has been affected by hydrothermal solutions with alteration halos that led to the formation of minerals along the streaks. There deposits are similar to MVT deposits as there are extremely low intensity areas of magnetic and gravity anomalies, shown on GIS maps prepared for the region. Such maps are overlaid with geological maps with faults locations to find the areas with mineral deposits, that include four regions. The areas of the deposits are found from the spatial intensity changes of gravity and magnetic anomalies. The lineaments based on magnetic anomalies have two directions, namely along the northwest-southeast and northeast-southwest. The gravity anomalies however show an east-west direction. According to the pictures, evident polarization in the magnetic field and less tangible polarization in the gravitational field do not show obvious changes in the contour maps. The first derivative operations highlight the high and low-intensity areas in the magnetic field and the gravitational field. According to this image the first derivative operations have similar results on both magnetic and gravity anomalies. The first derivatives of the anomaly fields show the spatial distributions of gravity and magnetic fields. By putting these images on the pattern of faulting and geological maps, it is clear that multiple gravity and magnetic lineaments match with the locus of regional faults. There is also a significant relationship between the mineral masses and the magmatic rocks in the area.