Volcanic Rocks from Q-Prospect, Chatree Gold Deposit, Phichit Province, North Central Thailand: Indicators of Ancient Subduction
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Arab J Sci Eng (2014) 39:325–338 DOI 10.1007/s13369-013-0839-z RESEARCH ARTICLE - EARTH SCIENCES Volcanic Rocks from Q-Prospect, Chatree Gold Deposit, Phichit Province, North Central Thailand: Indicators of Ancient Subduction Jensarin Vivatpinyo · Punya Charusiri · Chakkaphan Sutthirat Received: 17 May 2011 / Accepted: 15 February 2013 / Published online: 12 November 2013 © King Fahd University of Petroleum and Minerals 2013 Abstract Volcanic rocks exposed at Q-prospect in the northern Chatree gold deposit, Phichit province, Thailand, appear to have erupted during Permo-Triassic period; they are geochemically composed of basalt porphyry, basaltic tuff and rhyolitic/rhyodacitic tuff. These host rocks are often cross cut by basaltic andesite dyke. Zr/TiO2 versus SiO2 diagram indi- cates that these volcanic hosts are significantly equivalent to sub-alkali basalt and rhyodacite–rhyolite. Based on trace ele- ment compositions, they appear to have derived from tholei- itic magma originated within mantle and partially involved by crustal material; on the other hand, basaltic andesite dyke may have originated from calc-alkaline magma at a shal- lower depth within crustal environment. A tectonic model of subduction-related island arc is therefore suggested for magma evolution that also led to gold deposit. Consequently, it fits very well with the regional tectonic of the country. Keywords Gold deposit · Petrogenesis · Subduction · Tectonic · Thailand · Volcanism 1 Introduction The Chatree gold deposit, the largest deposit of Thailand, is located on the western edge of Khorat plateau in the north central part of the country. Geological setting of the area is mainly occupied by Pre-Jurassic volcanic rocks which have been discovered extensively in the northern highland, the western margin of the Khorat plateau and the eastern Gulf region (Fig. 1). The Pre-Jurassic volcanic rock can be sub- divided into three main belts including Chiang Rai–Chiang · · B J. Vivatpinyo P. Charusiri C. Sutthirat ( ) Mai, Chiang Khong–Tak and Loei–Phetchabun–Ko Chang Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand [1]. e-mail: [email protected]; [email protected] The Chiang Rai–Chiang Mai volcanic belt exposes along north–south direction from Chiang Rai province to Chiang C. Sutthirat Mai province in the north of the country (see Fig. 1). This Center of Excellence on Hazardous Substance Management (HSM), Environmental Research Institute, Chulalongkorn University, volcanic belt is composed of mafic lavas, hyaloclastites, pil- Bangkok 10330, Thailand low breccias and mafic dykes that appear to have erupted 123 326 Arab J Sci Eng (2014) 39:325–338 Fig. 1 Distribution of the volcanic rocks in Thailand and location of the study area [1] during the Permian to Permo-Triassic [2–5]. Mafic volcanic volcanic belt is composed of lavas and pyroclastics that have rocks in Chiang Rai area may have formed within a subduc- compositions ranging from felsic to mafic [1] and appears tion environment [6,7], whereas those in the Chiang Mai area to have locally occurred in different tectonic settings. The seem to have formed in an oceanic within-plate environment Permo-Triassic Phetchabun volcanic rocks erupted in arc- including mid-oceanic ridge and ocean islands [5,8]. magmatism related to subduction of paleotethyan oceanic East of Chiang Rai–Chiang Mai volcanic belt connects to crust beneath the western margin of the Indochina terrain the Chiang Khong–Tak volcanic belt which is significantly [12,13]. characterized by volcanic series of rhyolite, dacite, andesite The geological setting for this study is the Chatree gold and pyroclastic rocks [1]. These volcanic rocks appear to have deposit which appears to have occurred within the Permo- been related to arc environment [3,4,7,9–11]. The last belt, Triassic volcanic rocks of Loei–Phetchabun–Ko Chang Vol- Loei–Phetchabun–Ko Chang, occurs along NE–SW trend canic Belt [1,8,12–14] (see Fig. 1). The igneous rocks includ- lining from Loei province to Phetchabun province and from ing granodiorite and andesite are located mainly in the south- Nakhon Sawan to Chanthaburi provinces (see Fig. 1). This ern area; these rocks were suspected to associate within a 123 Arab J Sci Eng (2014) 39:325–338 327 Fig. 2 Geological map of the Chatree gold deposit and study area (Q prospect) showing NE–SW and NW–SE faults and sample locations from 14 drill holes, modified from [32] volcanic arc [15]. Moreover, [16,17] suggested that the Cha- to polymictic breccias and fine-grained volcanic clastics. The tree volcanic rocks are characterized by calc-alkaline magma uppermost unit of the succession is characterized by rhyolitic that may have formed tectonically as parts of strato-volcano tuff [17]. in subduction-related arc. Main structures of this area are The main purpose of this work is to examine petrochemi- mainly recognized within the NNE–SSW to N–S trends with cal characteristics of volcanic rocks in Q-prospect which lead a minor trend along N–E direction. The main focus of this to an interpretation of tectonic processes. study is the Q-prospect that is located at the northern part of the main mining area, A pit (Fig. 2). In general, volcanic rocks in this gold deposit mainly 2 Sample Collection and Methodology consist of lavas and their related pyroclastic rocks with some related sedimentary rocks. However, the coherent rocks Forty-three rock samples were collected from 14 drill cores have similar compositions varying from andesite to rhyolite within Q-prospect (Fig. 2). Thirty thin sections were made (Fig. 2). The lava flows, which are predominantly porphyritic for petrographic study under polarizing microscope. Twenty- andesite, present at the southern area whereas pyroclastic four least-altered samples were carefully selected for whole- rocks appear to be widely spreading throughout the A, A– rock analyses including major and some trace elements using East, and Q prospects within the northern deposit. Rhyolitic X-ray fluorescence (XRF) spectrometry. Trace and rare earth ignimbrites and polymictic breccia also distribute through- elements were carried out by inductively coupled plasma– out the area with various proportions. The succession of mass spectrometry (ICP–MS) at Akita University in Japan. volcanic rock in the gold deposit can be described as por- These quantitative analyses were calibrated using rock stan- phyritic andesite at the lowest unit, followed by monomictic dards provided by the Geological Survey of Japan. 123 328 Arab J Sci Eng (2014) 39:325–338 All selected rock samples were crushed by an iron jaw Basaltic Andesite Dyke is the latest stage cutting through crusher prior to powdering using an agate mortar. Subse- basalt porphyry, basaltic tuff and rhyolitic/rhyodacitic tuff. quently, rock power samples were fused to glass beads for The dyke is green to dark green in color with scattered white XRF analyses of major oxides (i.e., SiO2,TiO2, FeOt ,MnO, spots (Fig. 3d). Microscopically, the rock has a hypocrys- MgO, CaO, Na2O, K2O and P2O5) and 10 trace elements talline texture, and contains 40% glass, 25% plagioclase, (i.e., Ba, Zn, Sr, Rb, Zr, Co, Cr, Ni, Y and V). Loss on igni- 15 % clinopyroxene, 10 % quartz and 10 % secondary min- tion (LOI) was also measured by weighting rock powders erals such as chlorite and epidote. Moreover, it shows sub- before and after ignition at 900 ◦C for 3 h in a TMF-200 ophitic texture and intergranular of coarser-grained plagio- electric furnace. Trace and rare earth elements were accom- clase and pyroxene (Fig. 3h) which may indicate shallow plished by ICP–MS (Agilent technology 7500 series) with intrusion. samples prepared by taking 0.1 g (±0.0001g) and dissolv- inginamixtureofHF–HNO3–HClO4 acid in sealed Teflon beakers. Detection limits range from 1 ppm to 0.01% for 4 Whole-Rock Geochemistry major oxides, 0.01–1 ppm for trace elements and 0.01 ppm for rare earth elements. Major, trace and rare earth elements of representative rock samples from the Q-prospect are summarized in Table 1. Detail of chemical characteristic is explained below. 3 Petrography Basalt Porphyry comprises low silica contents ranging from 43.77 to 51.07 wt% and moderate silica contents rang- Four rock units including basalt porphyry, basaltic tuff, rhy- ing from 54.82 to 58.36 wt%, which are mafic to interme- olitic tuff and basaltic andesite dyke were grouped and diate compositions. MgO contents range from 4.50 to 9.26 reclassified based on field investigation and petrography (see wt%. In addition, these rocks are rather low TiO2 contents Fig. 3). Petrographic descriptions of these rocks are reported (0.39–0.63 wt%), moderate Al2O3 contents (14.84–18.69 below. wt%), moderate to high K2O contents (2.36–10.43 wt%), Basalt Porphyry is generally greenish grey to dark green and low Na2O contents (0.19–1.61 wt%) compared to AGV- with white spots (Fig. 3a). Porphyritic texture is clearly 1[18,19]. Therefore, this rock type is generally classified, observed in these rock samples. Microscopically, phe- based on geochemical composition, as basalt. nocrysts are mainly composed of K-feldspar with subordi- Basaltic Tuff consists of SiO2 contents ranging from 46.31 nate plagioclase (Fig. 3e). Plagioclase and K-feldspar usually to 55.29 wt% and MgO contents vary from 4.77 to 9.23 wt%. show subhedral to euhedral crystals ranging in size from 0.5 These rocks have low TiO2 contents (0.43–0.56 wt%), mod- to 2mm long. These phenocrysts embedded in fine-grained erate Al2O3 contents (15.75–18.28 wt%), low Na2O contents groundmass of significant lath shaped feldspar subordinate (0.16–0.21 wt%) and extremely high K2O (6.98–10.12 wt%) opaque mineral. Feldspar laths usually form trachytic tex- compared to AGV-1 [18,19].