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 : 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, 10330, Thailand [1]. e-mail: [email protected]; [email protected] The Chiang Rai–Chiang Mai volcanic belt exposes along north–south direction from 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

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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 to 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

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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.

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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]. In general, the basaltic tuff has ture. In addition, both plagioclase and K-feldspar have been major oxides ranging within the same ranges of basaltic por- replaced slightly by sericite. The secondary minerals such as phyry (see Fig. 4). chlorite and calcite are also sometimes found in groundmass. Rhyolitic/Rhyodacitic Tuff is composed of moderate to Basaltic Tuff is commonly characterized by greenish to high SiO2 contents (67.10–78.19 wt%), high MgO contents dark green rocks (Fig. 3b) containing poorly sorted angular (0.76–3.33 wt%), low TiO2 contents (0.13–0.32 wt%), mod- to subrounded clasts which may reach up to 20% mode. eratetohighK2O contents (2.13–8.38 wt%) and low to mod- Clasts in these rock samples have different colors commonly erate Al2O3 contents (6.92–14.43 wt%) compared to RGM-1 green and reddish brown. Their sizes range from 0.05 to 2cm. [18–20]. Microscopically, plagioclase and K-feldspar are subhedral to Basaltic Andesite Dyke consists of 52.32–53.90% SiO2, euhedral with quantity of about 30% mode. Quartz usually 3.40–4.31% MgO, 0.90–1.18% TiO2, 16.45–17.12% Al2O3 occurs as angular fragments with amount of about 20 % mode and 3.26–4.32% Na2O. These rocks have relatively low K2O (Fig. 3f). This rock type shows patchy alteration to chlorite contents (av. 1.5 wt%) and high CaO contents (6.76–7.48 and sericite. wt%) compared to AGV-1 [18,19]. In addition, TiO2,CaO, Rhyolitic/Rhyodacitic Tuff has various colors usually from Na2O and P2O5 contents of these basaltic andesite dykes are white to pale pink and pale green (Fig. 3c). In general, their obviously higher than those of the former rocks; on the other constituents are composed of about 40% quartz crystal, 40% hand, their MnO and K2O contents are lower. ash and 20% lapilli; they appear to have been moderately to Harker-type variation plots of SiO2 against some major poorly sorted (Fig. 3g). Regarding to rock fragments, they are and minor oxides (e.g., TiO2,Al2O3, FeOt , MnO, MgO) and mainly characterized by basalt, andesite and rhyolite. Rock some selective trace elements (e.g., Co, V, Ni and Sc) appear samples in this group also show locally silicification. to have negative correlations (Fig. 4) between basalt por-

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Fig. 3 Mesoscopic photographs of: a basalt porphyry, b basaltic tuff, c rhyolitic tuff, d basaltic andesite dyke. Photomicrographs of e the basalt porphyry showing plagioclase (Pl) and K-feldspar (Kfs) phenocrysts and chlorite (Chl), f the basaltic tuff showing quartz (Qtz), plagioclase (Pl) and rock fragments (Rf), g the rhyolitic tuff showing fragmental quartz crystals (Qtz), K-feldspar (Kfs)androck fragments (Rf), h the basaltic andesite dyke showing intergranular of coarser-grained clinopyroxene (Cpx)and plagioclase (Pl) surrounded by quartz (Qtz) and glass with partly altered to chlorite (Chl)

phyry, basaltic tuff and rhyolitic/rhyodacitic tuff; however, P2O5, Sr, Zr, Nb, Hf and Th with lower contents of Rb and these may be influenced slightly by alteration process. On Ba than those of volcanic hosts (see also Table 1). the other hand, analyses of basaltic andesite dyke are clearly Classification diagram, plotting between SiO2 and Zr/TiO2 out of the relation trend. The basaltic andesite dykes are rel- [21], is applied for these rocks. In general, these vol- atively composed of higher contents of TiO2,CaO,Na2O, canic samples fall within various fields of rhyolite, rhy-

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Table 1 Major oxides (in wt%), trace and rare earth elements (in ppm) for the volcanic rocks from Q-prospect area Rock Basalt porphyry Basaltic tuff Sample Q-8 Q-7 A-34 A-35 Q-13 Q-4 Q-24 Q-9 A-36 A-38 Q-43 A-28

SiO2 47.62 48.53 44.30 43.77 51.07 58.36 54.82 48.55 46.31 52.92 53.61 55.29

TiO2 0.42 0.56 0.54 0.63 0.53 0.39 0.53 0.53 0.56 0.48 0.46 0.43

Al2O3 15.71 18.69 16.68 18.24 17.07 14.84 15.94 16.27 15.75 16.41 18.28 16.25 FeOt 10.33 10.18 9.94 10.12 8.06 7.10 8.10 8.33 10.84 8.82 8.16 9.59 MnO 0.23 0.31 0.18 0.17 0.44 0.33 0.43 0.30 0.48 0.46 0.31 0.28 MgO 7.89 5.31 8.76 9.26 4.50 5.20 5.23 9.23 6.97 7.34 5.08 4.77 CaO 3.58 0.81 3.45 3.61 2.20 0.94 2.28 0.83 3.19 0.23 0.36 0.24

Na2O0.19 0.30 1.44 1.61 0.19 0.67 0.19 0.20 0.15 0.20 0.21 0.16

K2O6.50 9.45 4.92 2.36 10.43 7.06 8.81 8.55 6.98 8.06 10.19 8.07

P2O5 0.03 0.12 0.15 0.14 0.12 0.08 0.12 0.11 0.09 0.06 0.09 0.08 LOI 6.76 5.19 7.29 9.74 4.40 3.78 3.22 6.12 7.06 4.40 3.64 4.58 Total 99.26 99.44 97.66 99.64 99.01 98.75 99.66 99.01 98.37 99.40 100.39 99.75 Sc 27.633.130.834.727.123.227.429.538.128.631.130.5 V 195 329 254 289 183 185 208 202.7 323.8 227.1 233.5 223.2 Cr 22.324.320.720.827.427.633.024.728.924.322.626.1 Co 32.126.831.729.121.121.421.628.829.722.218.021.6 Ni 11.011.413.815.014.08.914.413.810.912.07.88.9 Cu 63.083.775.747.3 177.335.4 228.646.682.650.8 112.029.4 Zn 49.044.0 105.8 109.767.430.376.057.5 111.8 151.956.4 166.9 Ga 17.018.416.318.019.516.519.317.417.720.120.315.3 Rb 90 148 61 42 141 93 129 108.994.683.6 153.4 111.7 Sr 77 139 225 111 173 134 179 95.8 109.2 120.0 938.778.4 Y16.213.18.28.611.48.813.47.76.43.76.86.3 Rock Rhyolitic/rhyodacitic tuff Basaltic andesite dyke

Sample A-27 Q-42 A-39 Q-22 A-33 Q-40 Q-14 A-31 Q-41 Q-17 Q-6 A-26

SiO2 78.19 76.30 76.22 71.79 73.06 72.87 67.10 67.88 69.69 67.18 52.32 53.90

TiO2 0.23 0.26 0.26 0.23 0.13 0.23 0.32 0.31 0.25 0.30 1.18 0.90

Al2O3 10.06 9.61 8.26 11.94 6.92 12.37 11.16 11.54 13.02 14.43 17.12 16.45 FeOt 2.98 2.83 5.19 2.99 2.15 3.18 4.12 5.25 3.40 3.74 8.89 7.45 MnO 0.02 0.11 0.10 0.07 0.26 0.03 0.16 0.17 0.13 0.07 0.14 0.15 MgO 1.28 0.76 1.09 1.45 3.33 1.14 1.74 2.97 3.24 0.95 3.40 4.31 CaO 0.40 0.75 1.07 1.95 4.29 0.34 3.41 1.27 0.54 1.05 6.76 7.48

Na2O0.12 0.22 0.14 2.26 0.12 0.19 0.16 0.16 0.18 0.20 4.32 3.26

K2O2.58 7.50 4.63 3.38 2.13 6.70 6.47 7.41 6.54 8.38 1.52 1.51

P2O5 0.07 0.09 0.06 0.06 0.04 0.06 0.10 0.07 0.07 0.06 0.30 0.23 LOI 3.25 1.42 1.81 3.22 7.00 2.71 4.06 2.60 2.80 3.22 2.24 3.83 Total 99.18 99.84 98.82 99.35 99.42 99.82 98.80 99.61 99.85 99.59 98.20 99.47 Sc 11.916.918.78.95.39.818.217.311.217.622.519.0 V 111.378.8 157.337.125.162.2 127.9 145.569.191.9 230.3 184.8 Cr 10.529.424.59.27.94.921.327.24.713.234.990.6 Co 5.614.213.34.13.26.011.712.04.96.323.323.4 Ni 3.910.36.02.13.22.28.010.61.75.718.439.4 Cu 17.750.336.329.812.412.618.448.16.527.5 100.979.6 Zn 54.641.235.233.238.527.724.558.7 100.2 114.440.576.8

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Table 1 continued Rock Rhyolitic/rhyodacitic tuff Basaltic andesite dyke Sample A-27 Q-42 A-39 Q-22 A-33 Q-40 Q-14 A-31 Q-41 Q-17 Q-6 A-26

Ga 8.6 7.6 8.1 10.7 8.1 13.9 12.7 12.9 13.3 14.3 21.2 19.8 Rb 38.0 101.7 67.3 56.9 26.1 115.6 94.0 96.7 92.3 124.5 22.8 20.7 Sr 28.7 53.3 53.3 104.6 73.3 105.8 62.7 39.4 66.6 122.4 638.4 392.2 Y 4.2 7.5 3.9 9.9 9.3 6.0 6.8 5.3 6.1 14.6 23.0 17.4 Rock Basalt porphyry Basaltic tuff

Sample Q-8 Q-7 A-34 A-35 Q-13 Q-4 Q-24 Q-9 A-36 A-38 Q-43 A-28

Zr* 46.9 37.9 28.0 30.8 56.1 42.1 51.4 25.4 27.8 24.2 48.6 30.9 Nb 0.9 0.9 0.8 0.7 1.2 0.9 0.9 0.6 0.4 0.6 0.9 0.3 Cs 0.2 1.3 1.4 3.1 0.6 0.2 0.5 0.6 1.1 0.3 0.5 0.8 Ba 1979 5241 919 64 1318 3797 3111 3138 1911 5467 2170 6086 Hf 0.6 0.5 0.4 0.4 0.7 0.5 0.6 0.3 0.3 0.3 0.6 0.4 Ta 0.2 0.2 0.3 0.3 0.3 0.2 0.3 0.2 0.2 0.2 0.2 0.2 Pb 1.0 1.1 7.0 2.5 2.1 1.2 1.7 9.9 1.3 3.1 2.2 2.1 Th 0.5 0.3 0.2 0.3 0.5 0.4 0.5 0.2 0.2 0.2 0.4 0.3 U 0.1 0.1 0.2 0.1 0.2 0.1 0.2 0.1 0.1 0.1 0.2 0.3 La 2.9 3.1 2.2 2.5 2.9 3.1 4.3 1.3 1.4 0.7 1.2 2.6 Ce 7.4 7.5 5.5 6.4 7.2 7.0 9.6 3.6 3.4 2.0 3.1 5.2 Pr 1.1 1.1 0.8 1.0 1.0 1.0 1.3 0.6 0.5 0.3 0.4 0.7 Nd 5.7 5.5 4.6 5.3 5.0 4.6 6.3 3.0 2.6 1.6 2.2 3.2 Sm 1.9 1.7 1.4 1.6 1.5 1.2 1.8 1.0 0.8 0.5 0.8 1.0 Eu 0.9 1.2 0.8 0.5 0.8 0.9 0.8 1.1 0.7 0.7 0.6 0.9 Gd 2.5 2.2 1.6 1.8 1.9 1.4 2.2 1.4 1.1 0.7 1.0 1.1 Tb 0.4 0.4 0.3 0.3 0.3 0.2 0.3 0.2 0.2 0.1 0.2 0.2 Dy 2.8 2.3 1.5 1.6 2.1 1.5 2.3 1.5 1.2 0.8 1.2 1.3 Ho 0.6 0.5 0.3 0.3 0.4 0.3 0.5 0.3 0.3 0.2 0.3 0.2 Er 1.8 1.5 1.0 1.0 1.4 1.1 1.5 0.9 0.8 0.5 0.9 0.8 Tm 0.3 0.2 0.2 0.1 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.1 Yb 1.8 1.4 1.0 1.0 1.4 1.1 1.5 0.8 0.7 0.6 1.0 0.8 Lu 0.3 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.2 0.1 Rock Rhyolitic/rhyodacitic tuff Basaltic andesite dyke

Sample A-27 Q-42 A-39 Q-22 A-33 Q-40 Q-14 A-31 Q-41 Q-17 Q-6 A-26

Zr* 31.8 25.8 22.0 49.9 37.9 46.5 30.3 28.2 40.3 88.4 151.3 127.3 Nb 0.2 0.5 0.5 0.9 0.8 1.2 0.6 0.6 0.8 1.8 4.3 3.2 Cs 0.8 0.2 0.6 0.8 0.6 1.9 0.7 0.2 0.9 1.5 0.1 0.1 Ba 297 1085 1251 721 466 1400 941 1100 1356 575 235 304 Hf 0.3 0.3 0.2 0.7 0.4 0.7 0.4 0.3 0.5 1.3 1.9 1.6 Ta 0.1 0.1 0.1 0.1 0.1 0.2 0.1 0.1 0.2 0.2 0.4 0.4 Pb 1.6 1.4 3.4 2.7 2.8 6.1 1.9 0.7 1.2 3.1 4.6 4.1 Th 0.3 0.2 0.2 0.7 0.5 0.6 0.3 0.2 0.6 1.1 1.4 1.2 U 0.3 0.1 0.1 0.3 0.4 0.3 0.1 0.1 0.2 0.7 0.5 0.4 La 1.3 1.8 1.2 4.9 4.0 1.8 3.1 1.4 1.7 3.6 13.0 10.9 Ce 2.8 4.4 2.8 10.4 9.3 4.4 7.4 3.4 3.8 8.7 31.2 26.0 Pr 0.4 0.6 0.4 1.4 1.3 0.6 1.1 0.5 0.5 1.2 4.4 3.6 Nd 2.0 3.0 1.9 6.3 5.6 2.9 5.1 2.6 2.5 5.5 20.0 16.1

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Table 1 continued Rock Rhyolitic/rhyodacitic tuff Basaltic andesite dyke Sample A-27 Q-42 A-39 Q-22 A-33 Q-40 Q-14 A-31 Q-41 Q-17 Q-6 A-26

Sm 0.70.80.61.61.50.71.40.90.71.65.03.8 Eu 0.30.50.40.60.60.50.60.40.50.41.41.2 Gd 0.81.10.71.71.70.91.51.00.91.95.43.9 Tb 0.10.20.10.20.30.10.20.20.10.30.80.6 Dy 0.81.20.71.71.51.11.31.00.92.64.53.3 Ho 0.20.30.20.40.30.20.30.20.20.60.90.6 Er 0.50.90.51.20.90.90.80.70.82.12.51.9 Tm 0.10.10.10.20.10.10.10.10.10.30.30.2 Yb 0.60.90.41.30.91.00.70.70.92.32.21.6 Lu 0.10.10.10.20.10.20.10.10.10.40.30.2 Major oxides and Zr* analyzed by XRF odacite/dacite, andesite and sub-alkali basalt (Fig. 5a). arc environment [26]. Moreover, Fig. 7 also shows that basalt According to discrimination diagram of Y versus Zr (less porphyry, basaltic tuff and rhyolitic/rhyodacitic tuff are com- mobile trace elements) [22] shown in Fig. 5b, it clearly indi- parable to an island-arc tholeiite [27], while the younger cates that most of volcanic rocks from the study area related basaltic andesite dyke has composition very similar to island- to tholeiitic magma, whereas two samples of basaltic andesite arc calc-alkaline [27]. dyke are characterized by transitional/calc-alkaline magma Very high K positive anomaly (Fig. 7a–c) for basalt por- series (Fig. 5b). It should be notified that these samples were phyry, basaltic tuff and rhyolitic/rhyodacitic tuff appears to taken from dill cores; therefore, number of dyke was limited. have been involved by feldspar accumulations that are com- The chondrite [23] normalized REE patterns of basalt por- patible to Eu anomalies appeared on REE patterns mentioned phyry and rhyolitic/rhyodacitic tuff show gentle slopes and above. In addition, high field strength elements plotting Th– have low fractionated LREE patterns with average (La/Yb)N Hf–Nb diagram [28] and La–Y–Nbdiagram [29] also classify ratios of about 1.58 and 1.79, respectively (Fig. 6a, c). The these rocks as arc environment (Fig. 8a, b). For Ti–V varia- basaltic tuff presents almost flat patterns with an average tion diagram [30] (Fig. 8c), it can separate basaltic andesite (La/Yb)N ratio of 1.25 (Fig. 6b). These may be results of dyke (MORB/BAB) from all host rocks (island arc tholeiite). high degree of partial melting for magma generation of the- In addition, Nb/Yb versus Th/Yb diagram [31] suggests that ses volcanic rocks; besides, they appear to have derived from basalt porphyry, basaltic tuff and rhyolitic/rhyodacitic tuff a deep mantle-rich source. On the other hand, patterns of may have originated in oceanic arc environment, whereas the basaltic andesite dykes show significantly LREE enrichment basaltic andesite dykes are plotted at the boundary between yielding an average (La/Yb)N ratio of about 4.23 with low- oceanic arc and continental arc (Fig. 8d). Although samples negative Eu anomalies (Fig. 6d) that would be effected of of basaltic andesite dyke were limited as mentioned earlier, lower degree of partial melting comparing to the former they appear to have different provenance from those of the groups. In addition, most patterns of the former rocks show host volcanic rocks. similarly high-positive Eu anomalies (Fig. 6a–c). The Eu+2 is compatible in feldspar crystallization [24]; these are cor- responding to geochemical and petrographic data of these 5 Discussions and Conclusions host rocks which usually contain high K2O contents and K- feldspar compositions. Therefore, these evidences indicate Volcanic and pyroclastic rocks found within Q-prospect of that their initial magma may have feldspar crystallization and Chatree gold deposit is composed of a sequence of basalt accumulation during transportation to the surface. It should porphyry, basaltic tuff and rhyolitic/rhyodacitic tuff from have been at least stored somewhere prior to eruption which bottom to top, respectively. Moreover, they are cross cut provided a period of crystal fractionation and magma dif- by the younger basaltic andesite dyke. The sequence gen- ferentiation yielding composition range between basalt and erally appears to be similar to those observed throughout the rhyolite. Primitive mantle [25] normalized patterns of these deposit [17]. All volcanic and pyroclastic rocks have simi- rocks show many spikes of Ba, U, K, and Sr with trough of lar chondrite-normalized REE patterns showing very gentle Nb (Fig. 7); they indicate magma evolution in a magmatic- slopes that indicate high degrees of partial melting, prob-

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Fig. 4 Harker diagrams plotting between SiO2 versus major oxides and some trace elements

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Fig. 5 Classification and discrimination diagrams. a Zr/TiO2 versus ination diagram [22] showing composition ranges of samples mainly SiO2 diagram [21] showing rock samples fallen mainly within fields tholeiitic to subordinately transitional and calc-alkaline (same symbols of rhyolite/rhyodacite, andesite and sub-alkali basalt, b Y–Zr discrim- used in Fig.4)

Fig. 6 Chondrite [23] normalized REE patterns of a basalt porphyry, b basaltic tuff, c rhyolitic/rhyodacitic tuff and d basaltic andesite dyke

ably >20% compared to those reported by Rollinson[24]. The results of this study indicate that volcanic and The younger basaltic andesite dyke clearly has LREE enrich- pyroclastic rocks of Q-prospect, including basalt porphyry, ment that suggests a low degree of partial melting. Primitive basaltic tuff and rhyolitic/rhyodacitic, appear to have orig- mantle-normalized patterns of all rock types have positive inated within an island-arc volcanic environment. Tholei- anomalies of Ba, U, K and Sr with negative anomaly of Nb itic magma is possibly an initial source prior to magma dif- which seem to be a characteristic of island-arc environment ferentiation that yields various volcanic rocks ranging from [27]. basaltic to rhyolitic compositions. Age dating of porphyritic

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Fig. 7 Primitive mantle [25] normalized spider diagrams of a basalt porphyry, b basaltic tuff, c rhyolitic/rhyodacitic tuff and d basaltic andesite dyke. a–c Compared with a pattern of island arc tholeiite [27]andd is compared with island arc calc-alkaline [27]

Fig. 8 Tectono-diagrams of a Th–Hf–Nb [28], b La–Y–Nb [29]andc Ti–V [30] showing arc-related environment; besides, d Nb/Yb and Th/Yb plots [31] separating basaltic andesite dyke from the host volcanic rocks within arc environment

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Fig. 9 Tectonic evolution models of Chatree volcanic rocks, Phichit–Phetchabun provinces

andesite from the same deposit yielded 250 ± 6 Ma whereas of volcanic hosts and dyke indicate clearly different mag- the younger dyke gave an age of 244 ± 7Ma [32]. They matic sources and degree of partial melting; however, they may be assumed to have originated within the same period. appear to be related to the same subduction zone. Regarding Based on data gained from this study, the basaltic andesite the parent of the volcanic hosts, they have various composi- dyke may be related to calc-alkaline magma originated within tions which are geochemically related to the same source of the same island arc environment in which most magmas of high mafic provenance closely related to island arc tholei- the host volcanic rocks appear to have developed continu- ite; however, magmatic differentiation may have continu- ously. These geneses fit quite well with the tectonic model ously taken place yielding composition ranging from basalt to of Thailand [12,33–35]. These volcanisms would have been rhyolite. formed as a consequence of eastward subduction of the The Permo-Triassic volcanic rocks along the Loei– Lampang–Chiang Rai oceanic plate (or slab) beneath the Phetchabun–Ko Chang volcanic belt can be subdivided into Nakhon Thai oceanic plate during Permo-Triassic Period two sub-belts, i.e., Tha Li-Wang Sai Phun (covering the forming an island-arc environment [15]. During this period, study area)-Lop Buri-Chantaburi volcanic sub-belt (western high degree of partial melting may have taken place leading part) and Phetchabun-Saraburi-Sra Kaeo volcanic sub-belt to tholeiitic magma generations in mantle (Fig. 9) and sub- (eastern part) [36]. These volcanic sub-belts can be sepa- sequent eruptions of all volcanic of the study area as well as rated based on their petrochemistry and mineralization data. the adjacency. Higher alkaline composition of calc-alkaline The first sub-belt is located along Tha Li district, western basaltic andesite dyke may have occurred at a shallower depth Loei province southward to Wang Sai Phun district, Phichit of crust which was heated by the prior tholeiitic magma and province, and Lop buri to Chantaburi provinces. The sec- promptly led to lower degree of partial melting of the existing ond sub-belt is exposed in Phetchabun province southward magmatic arc and as well as assimilate intra-arc sediments to and Sra Kaeo province, respectively. and previous volcanic rocks, while undergoing fractional The volcanic rocks in both sub-belts had erupted in a sub- crystallization to generate calc-alkaline andesitic magma of duction environment. The volcanic rocks in the first sub-belt the dyke rocks (Fig. 9). REE patterns and spider diagrams were formed within an island arc volcanism [15,37, and this

123 Arab J Sci Eng (2014) 39:325–338 337 study] and it is significantly associated with Au–Ag–Pb–Zn References mineralization [1,32,37]. On the other hand, the second sub- belt erupted in a continental volcanic arc [13,38–40]. These 1. Jungyusuk, N.; Khositanont, S.: Volcanic rocks and associated min- evidences clearly indicate that the tectonic model and evolu- eralization in Thailand. In: Proceedings of the National Conference on Geologic Resources of Thailand: Potential for Future Develop- tion of ancient subduction-related island arc toward the east- ment, Bangkok, pp. 528–532 (1992) ern continental arc before all tectonic terranes were welded 2. Chuaviroj, S.; Chaturongkawanich, S.; Sukawattananan, P.: Geol- completely. These tectonic processes appear to have occurred ogy of Geothermal Resources of (Part I, San continuously and produced extensive volcanism of the coun- Kamphaeng). 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