زمین‌ شیمی سنگ کل و شیمی‌ بلور آپاتیت در دنباله های نفوذی ناحیه قینرجه- انگوران (غرب زنجان): رویکردی برای شناسایی گرانیتوئیدهای مولد اسکارن و تحولات ماگمایی- فلززایی

ناحیه قینرجه- انگوران در محل تلاقی پهنه‌های ساختاری ارومیه- دختر و سنندج- سیرجان، در شمال غرب ایران جای دارد. در این ناحیه دنباله های نفوذی با سن تریاس میانی- ژوراسیک بالایی شامل توده کوارتزدیوریت قراول خانه، واحد گرانیت پورفیری کوه بلقیس و توده گرانودیوریتی قینرجه رخنمون دارند. این پژوهش به واکاوی داده‌های زمین‌شیمی سنگ کل و شیمی‌بلور آپاتیت در دنباله های نفوذی یادشده برای دستیابی به تحولات زمین‌شیمیایی- فلززایی ماگما و مقایسه شاخص های باروری توسط درون یابی عناصر کمیاب می پردازد. توده های مورد بررسی با دمای همگنی زیرکن (tzr) کمتر از 900 درجه سانتی‌گراد و ماهیت متاآلومین تا کمی پرآلومین (a/cnk = 0.5-1.2) متعلق به سری کالک آلکالن هستند که شواهد گرانیتوئیدهای نوع i (na2o/k2o = 0.8-2.0) محیط های فرورانش (غنی شدگی lile نسبت به hfse همراه بی هنجاری های p، nb و ti) را نشان می دهند. تمرکز σree نسبت lree/hree و محتوای lile (شامل مجموع عناصر rb، ba، th، u، k و pb) در گرانودیوریت های قینرجه به طور متوسط دو برابر توده های دیگر تعیین‌شده است که جای‌گیری در عمق 20 تا 30 کیلومتری پوسته (sr/y = 10-20) نسبت rb/sr سنگ کل کمتر از 4/0 و محتوایfeo  حدود wt.% 4، ویژگی اسکارن های آهن دار را نشان می دهد. طبق شواهد ریزکاوالکترونی، آپاتیت های کوارتزدیوریت قراول خانه با تمرکز بالای فلوئور (f = 2.2-2.7 wt.%) به طور مستقیم از ماگمای نخستین و آپاتیت های گرانیت پورفیری کوه بلقیس با تغییرات بالای کلر (cl = 0.52-0.65 wt.%) در نتیجه تبادلات وسیع سیال- سنگ میان توده گرانیت پورفیری و سیال گرمابی شکل گرفته اند. در مجموع، توده گرانودیوریتی قینرجه و پس از آن کوارتزدیوریت قراول خانه بیشترین شباهت را با الگوی پتروژنز- فلززایی توده های مولد ذخایر اسکارن آهن نشان می دهند.

whole-rock geochemistry and crystal chemistry of apatite at intrusive suites of the qeynarjeh-angouran district (west of zanjan): an approach to the identification of skarn-causative granitoids and magmatic-metallogenic evolutions

the qeynarjah-angouran district is located at the intersection of the urumieh-dokhtar and the sanandaj-sirjan structural zones in nw iran. in this area, intrusive suites of middle triassic-upper jurassic age are exposed, including the gharavol-khane quartz diorite, the kuh-e belghais granite porphyry, and the qeynarjeh granodiorites. whole-rock geochemical data and crystal chemistry of apatite were analyzed to obtain the geochemical-metallogenic evolutions of magma and compare fertility using trace element interpolation. these intrusive suites with zircon saturation temperature (tzr) less than 900 °c and meta-aluminous to slightly peraluminous nature (a/cnk = 0.5-1.2) belong to the calc-alkaline series, which is evidence of i-type granitoids (na2o/k2o = 0.8-2.0) in subduction zones (enrichment of lile compared to hfse along with p, nb and ti anomalies). σree concentration, lree/hree ratio, and lile content (including rb, ba, th, u, k and pb elements) in the qeynarjeh granodiorites are determined to be twice as much as other intrusive suites, which are placed at a depth of 20 to 30 km of crust (sr/y=10-20), rb/sr ratio of whole-rock less than 0.4 and feo content about 4 wt.% indicate characteristics of ore-bearing skarns. epma results show apatite crystals from gharavol-khane quartz diorite with high fluorine concentration (f = 2.2-2.7 wt.%) have been formed directly from the parent magma and kuh-e belghais granite porphyry apatites with high chlorine variation (cl = 0.52-0.65 wt.%) is a result of large fluid-rock interactions between the granite porphyries and hydrothermal fluids. overall, the qeynarjeh granodiorites and the gharavol-khane quartz diorites show the most similarity with the petrogenesis-metallogenesis pattern of the iron skarn-causative intrusions. introduction and geological background chemical composition, origin, and magmatic‒metallogenic evolution of intrusive suites with granitoid nature have a significant role in evaluating mineral potential and separating fertile and barren intrusive rocks in orogenic belts (svetlitskaya and nevolko, 2022). determining the physicochemical characteristics of granitoids such as temperature, pressure, oxygen fugacity (logfo2), and volatile elements (e.g., water content, chlorine, and sulfur oxide) is necessary to investigate the relationship between the formation of intrusive suites and mineralization (richards and kerrich, 2007; wang et al., 2014; zhu et al., 2018; zhang et al., 2022). determination of these characteristics is important, especially for evaluating magmatic‒hydrothermal systems and the skarn-causative granitoid deposits (e.g., porphyry and skarn deposits). the takab-angouran belt in the northwest of iran hosts numerous mineral deposits from neoproterozoic to cenozoic, some world-class deposits (e.g., angouran zinc and zarshoran gold deposits) have been formed in this area. the enormous magmatic-hydrothermal-geothermal eruptions caused by the closing of the big neotethys sea and the occurrence of the zagros mountain belt have led to the formation of a large volume of granitoid and volcanic intrusive suites with the age range of triassic-jurassic to miocene in the takab-angouran. in this research, the whole-rock geochemical data and chemistry of apatite in gharavol-khane quartz diorite, kuh-e belghais granite porphyry, and qeynarjeh granodiorite have been evaluated from the point of view of iron skarn potential. the purpose of this research is to achieve magmatic control factors and compare the fertility indicators of granitoids using the trace element ratio and geochemical diagrams in the intrusive suites. also, petrography and apatite crystal chemistry have been used to obtain the petrogenesis-metallogenesis pattern of granitoids. this evidence could be helpful in advancing exploration programs and identifying encouraging mineral areas in the qeynarjeh-angouran area. material and methodsafter studying geological maps and conducting detailed sampling, field works, and sampling of different rock units were conducted. therefore, 80 rock samples were taken from various intrusive suites, and after petrographic studies, 20 fresh samples were selected. petrographic studies were carried out using a zeiss reflected-transmitted polarizing microscope (axioplan2 model). for chemical analysis, 10 samples of gharavol-khane quartz diorite, 5 samples of kuh-e belghais granite porphyry, and 5 samples of qeynarjeh granodiorite were selected and grounded in agate pounder to 200 mesh size (about 75 micrometers). whole-rock geochemical data has been carried out in the geochemistry laboratory of istanbul university of technology, by x-ray fluorescence (wdxrf) wavelength-based model s8 tiger to detect the main oxide elements (in terms of wt.%) and inductively coupled plasma mass spectrometer (icp-ms), elan drc-e model for identification of minor and rare earth elements (in terms of ppm). digestion of samples (approximately 50 mg) has been done in two steps: 1) by 6 ml of hcl acid (37% concentration), 2 ml of hno3 acid (65% concentration), and 1 ml of hf acid (concentration 38-40 percent), and 2) the destruction of the remaining refractor minerals by adding 6 ml of b(oh)3 acid (concentration 5%). destruction of the samples was done in a berghoff model microwave teflon pot at a temperature of 135 °c. the analysis accuracy surpasses 2% for major elements and surpasses 5% for rare elements. to obtain the chemical composition of apatite types in the study intrusive suites, about 30 points were tested by electron microprobe analysis (epma) model jeol jxa-8530f in the laboratory of the german geosciences research center (gfz). spot analysis was performed with a 15kv voltage, an electron beam current of 5 na, a beam diameter of 10 microns, and an irradiation time of 5 to 10 seconds. the x-ray geometry jump angle of the device is between 50 and 60 degrees, and the analysis error is less than 10 grams per ton. results and discussionthe intrusive suites of the studied area include the gharavol-khane quartz diorite intrusion with granular and porphyroidic textures, the kuh-e belghais granite porphyry with porphyry, granular and graphic textures, and the qeynarjeh granodiorite, has microgranular, porphyroidic, and graphic textures. in terms of alumina saturation index (asi), the study intrusive suites belong to the metaluminous to slightly peraluminous series and i-type granite and have calc-alkaline to shoshonitic affinity. an enrichment of lile compared to hfse was observed in the study area, and this enrichment occurred during melting due to the high ionic potential of lile and the decrease in solubility of hfse in aqueous fluids. a negative anomaly in eu and a positive anomaly in ce were observed, which occurred due to low-oxygen fugacity and increased eu+2/eu+3 and ce+3/ce+4 ratios in the silicate melt. three types of apatite: ap1 (with elongate habit and homogeneous appearance in the gharavol-khane quartz diorite), ap2 (subhedral to anhedral form in the kuh-e belghais granite porphyry), and ap3 (anhedral to subhedral form in the qeynrajeh granodiorite), were recognized in qeynarjeh-angouran district. all apatites belong to the hydroxy-fluorine apatite class and originated from magmatic origin. ap1 crystals were formed directly from the parent magma but ap2 and ap3 crystals were formed during skarnization. the intrusive suites of the studied area, have the characteristic signatures of subduction zone magmas in a volcanic arc setting. qeynarjeh granodiorite is ore-bearing, kuh-e belghais granite porphyry is non-productive, and gharavol-khane quartz diorites are barren to ore-bearing nature and they are all in the range of mineralized differentiated intrusive in-depth. the qeynarjeh granodiorite is an ore-bearing granite and shows evidence of a skarn-causative suite (non-porphyry). acknowledgementsthis research has been done with the support of the bu-ali sina university. the authors are grateful for the useful comments of the reviewer of economic geology journal.