CHAPTER 1 Introduction

CHAPTER 1

Introduction

1.1 Purpose and Scope of the Study

Igneous rocks at the Doi Kio Lom (DKL) area, Pai district, Mae Hong Son province northward extents from Samoeng granite through Chaing Dao and Pai granite. These granitic rocks are associated with mineral deposits in northern Thailand especially tin- tungsten and fluorite deposit (Department of Mineral Resources, 1971; Cobbing and Pitfield, 1985; Cobbing et al., 1986; 1992; Schwartz et al., 1995). The aim of this study is to discuss the evolution of igneous intrusion, mineralization and alteration of the Doi Kio Lom area. The granitic rocks at the DKL and adjacent areas will be collected for petrographic and ore microscopic study, use for systematic classify igneous rock type, their texture and alteration. Whole rock geochemistry (major-, minor-, trace-, and rare earth elements) of least altered rocks will be analyzed to clarify rocks type and magmatic evolution. Zircon U-Pb age dating will be analyzed to determine the ages of crystallization.

1.2 Granitic Rocks in northern Thailand

The Granitic Rocks in northern Thailand (Fig. 1.1) distribute from Myanmar border continuing southward through Mae Hong Son province to Inthanon metarmorphic core complex in Chiang Mai province. They mainly compose of the Central granitic rocks that associated with migmatitic core complex or Doi Inthanon metamorphic core complex (Maldonald et al., 1991; Dunning et al., 1995; Macdonald et al., 2011) that flanked by east and west margin of plutons and small batholiths (Cobbing and Pitfield, 1986; Cobbing et al., 1992) and minor Eastern Belts and Western Belts granitic rocks.

Fig. 1.1 Geological map of northern Thailand showing distribution of granitic belts and the study area (after Cobbing, 2010 and Macdonald et al., 2011).

1.2.1 Eastern Granitic Belt

The Eastern Granitic Belt generally emplaced in Upper Paleozoic sedimentary and volcaniclastic sequences. These granite rocks mainly I-type affinity (Cobbing, 2011), comprised mainly two feldspars (alkali-and calcium-rich) with greenish brown to green color of mafic minerals and biotite (Charusiri et al., 1993). Geochemistry of this belt comprises calc-alkaline I-type or magnetite series (Ishihara et al., 1980) to I-S granites (Mahawat, 1982; Charusiri, 1989; Charusiri et al., 1993; Cobbing, 2011). Mahawat (1982) and Charusiri (1989) studied geochemistry of the Eastern Granitic Belt indicated that these granitiod rocks originate form differential crystallization or partial melt from true magma. Khositanont et al. (2007) the study of Lampang-Phrae granites suggest these granites were formed from lower crustal source with less contamination from upper crust when gradually cooling crystallization process in convergent plate margin. From 40Ar/39Ar technique has been found that ages of granites range from 210 – 245 Ma. (Charusiri et al., 1993). The U-Pb zircon age dating yielded ages 224±4 Ma and 228±3 Ma at Lampang-Phrae granites (Khositanont et al., 2007)

The largest body is Tak batholith that has been studied by Teggin (1975), Mahawat (1982) and Yokart et al. (2003) reported that Tak batholith is mainly I- type affinity comprised of hornblede-bearing diorite to granodiorite with inner monzogranite in the east of pluton, the west is biotite monzogranite and an inner is hornblende-biotite quartz monzonite. From Rb-Sr whole-rock isochron yielded 213±10 and 219±12 Ma for white and pink granite respectively (Beckinsale et al., 1979). Khositanont (2007) reported that Tak batholith yielded a zircon age of 228±3 Ma. Small plutons are also scattered in Phrae, Nan, Lampang and Loei provinces. Doi Ngom pluton in Phrea province is small isolated body, with pinkish-grey, biotite-hornblende granodiorite associated with Sb-W-Cu-F ore deposit. 40Ar/39Ar dated the age of tungsten at Doi Ngom is 35 Ma that much younger than the age of emplacement

1.2.2 Central Granitic Belt

The Central Granitic Belt occurs as a large batholith covers almost north of

Thailand, distributed from Myanmar border continuing south through Chiang Rai, Mae Hong Son, Chiang Mai to Lamphun and Lampang province. These granitic rocks mainly emplaced in Late Triassic to Early Jurassic (Beckinsale, 1979; Cobbing et al., 1986, 1992; Dunning et al., 1995; Darbyshire, 1988; Charusiri et al., 1993). Geochemistry of the Central granitic belts are S-type affinity, peralumiouns potassic (Cobbing et al., 1992; Charusiri et al., 1992, 1993; Imai et al., 2008; Ishihara et al., 2008) and shows highly evolved with high silica content and the high 87Sr/86Sr ratio of the central granite indicated a crustal derivation. This granitic belt is occurred associated with migmatitic core complex (Doi Inthanon metamorphic core complex) (Maldonald et al., 1991; Dunning et al., 1995; Macdonald et al., 2011) that flanked by isolate plutons and small batholith (Cobbing and Pitfield, 1985; Cobbing et al., 1992). The Doi Inthanon metamorphic core complex comprised of highly deformed and high grade metamorphic rocks. These rocks are orthogneiss, paragneiss, granitic mylonite and calc-silicate gniess (Maldonald et al., 1991; Dunning et al., 1995; Rhodes et al., 1997, 2000; Macdonald et al., 2011) which first led to inferred to Precambrian age (Baum et al., 1970; Pongsapitch et al., 1983). However, recent studies reported that the granites and associated migmatite have been assigned to Permo- Triassic age (Cobbing et al., 1986, 1992; Darbyshire, 1988; Pitfield, 1988; Dunning et al., 1995). Moreover, small undeformed plutons/batholiths have been studied by many authors (e.g. Baum et al., 1970; Cobbing and Pitfield, 1986; Cobbing et al., 1992). Eastern Marginal pluton/ batholiths distributed east side of the metamorphic core complex, in Chiang Rai province, east of Chiang Mai province to Li district, Lamphun province. These plutons emplaced into Silurian to Triassic rocks, mainly comprised of medium to coarse-grained K-feldspar megacrystic granite, megacrystic biotite granite, mainly S-type affinity with initial ratio 87Sr/86Sr 0.7280-0.0066 (Fang batholith), 0.7248±0.0014 (Khuntan batholith) (Cobbing et al., 1992) suggested form in syn-collision setting (e.g. Bunopas, 1981; Bunopas and Vella, 1983; Barr and Macdonald, 1991), with Rb-Sr whole- rock yielded age 240±64 Ma. at Fang batholith and 202±3 Ma at Khuntan batholith (Beckinsale, 1979). The western marginal granites formed a discontinuous chain of pluton in the west of the Inthanon metamorphic core

complex, distribute in Mae Cham district, Chiang Mai province and Mae Sariang district, Mae Hong Son province. The main component of the western margin is K-feldspar megacrystic biotite-hornblende granite with cognate microdiorite enclaves and small mafic clots. Geochemically, K/Ar biotite age dating yielded 186-207 Ma (Teggin, 1975) and 255 Ma from K/Ar amphibole technique. Braun et al. (1976) suggest 205 Ma from K/Ar biotite age dating or Triassic age.

Granitic rocks associated with the Doi Inthanon metamorphic core complex are composed of highly deformed rocks with leucosomes and mafic palaeosomes and formed migmatitic character with some undeformed granitic rocks. Some batholith/plutons in this area host Cretaceous granitic rocks. The deformed granite is weakly to strongly foliated equigranular and inequigranular to K-feldspar megacrystic biotite±muscovite granite (Ishihara et al., 1980; Cobbing et al., 1986; Kosuwan and Nakapadungrat, 1992), whereas undeformed granite is main phase of the Central Granitic Belt (Baum et al., 1970). The granite is medium- to coarse- grained porphyritic biotite granite intruded by minor phase of medium-grained two mica and fine-grained tourmaline-muscovite granites. Plutonic rocks in this area including Fang-Mae Suai (Baum et al., 1970; Cobbing and Pitfield, 1986), Doi Saket-Wiang Pa Pao (Nakapadungrat et al., 1984; Cobbing and Pitfield, 1986) Samoeng (Teggin, 1975; Cobbing and Pitfield, 1986). The age of granitic rocks from Rb-Sr whole rock isochron yielded 201±22 Ma (Beckinsale, 1979), and from K-Ar biotite ages for vinicity of the Samoeng mining range from 71-43 Ma (Teggin, 1975). Additional, the partial overprinting affected on these granitic plutons at Omkoi yielded age 46.2±2.3 Ma or Tertiary age (Department of Mineral resources, 1986).

The main mineralizations in the Central Granitic Belt are tin, tungsten, and fluorite related to Late Triassic-Early Jurassic granitic rocks and/or affected by hydrothermal alteration in Cretaceous (Beckinsale, 1979; Cobbing et al., 1986, 1992). Mineral deposits in northern Thailand associated with the Central Granitic Belts are occurred in Pai district, Mae Sariang district, Mae Hong Son province, Samoeng batholith, Omkoi pluton in Chiang Mai province, Li pluton, Khutan batholith in Lamphun-Lampang province, Wiang Pa Pao pluton/Mae Suai pluton

in Chiang Rai province. The deposit types in Late Triassic – Early Jurassic are mainly hydrothermal veins and contact metamorphism (Department of Mineral Resource, 1985; 1986; Nakapadungrat and Putthapiban, 1992). However, mineralization associated with Cretaceous and/or Tertiary granite is also occurred in north Samoeng pluton, Chiang Mai Province (Beckinsale, 1979; Cobbing et al., 1992). Thermal activity of Cretaceous/Tertiary granite was dated during 71-43 Ma (from K-Ar method) by Teggin (1975) and 49±1 Ma biotite K-Ar age by Cobbing et al. (1992). Tin-tungsten deposit occurs as hydrothermal type, pegmatite, quartz- feldspar veins, aplite, and contact metasomatic zone (Deparment of Mineral Resource, 2003). Samoeng tin-tungsten mineralizations are pyrometasomatic, pegmatitic, aplitic, greisen and quartz vein deposit (Boonyuen, 1981). The geochemical studies of the deposit suggested SiO2 and K2O increasing with magmatic differentiation; while CaO, MgO, Al2O3, TiO2 and Fe2O3 are decreased. Tin exhibited a closed relationship with differentiation and tungsten was controlled by calcium content in calcareous metasediments in contacted zone. Fluid inclusion and oxygen isotope studies of the Samoeng deposit indicated temperature of vein style cassiterite was deposited ranging between 350 and 470 °C and pressures between 1 and 2.4 Kb (Khositanont, 1990). A model for Samoeng Sn-W mineralizaion was meteoric water-dominated hydrothermal fluids, driven by the leucogranite intrusion, interacted with ilmenite-series, S-type granites. Khuntan tin-tungsten deposit in the Muang Yao unit is associated with Sn-W mineralization that consists of coarse- to medium-grained muscovite and muscovite-tourmaline granite and ore body form as greisen vein. Geochemical data for the Muang Yao unit differed from felsic S-type granite e.g. Rb-Yb-Nb enrichment and Ba-Sr-Zr depletion that could be a result of late stage fluid alteration (Yokart et al., 2003). The vein type Sn-W deposit presented from an endogranite vein system to proximal-intermediate vein system of magmatic- hydrothermal origin. The age of mineralization from Rb-Sr isochron yielded age of 202±3 Ma (Cobbing et al., 1992). Ore deposits associated to Cretaceous and/or Tertiary granite e.g. Doi Mok cassiterite-scheelite deposits and Mae Che Di tungstens deposit in Wiang Pa Pao granite were reported (Nakapadungrat and Putthapiban, 1992; Crow and Khin Zaw, 2011). Moreover, fluorite deposit

occurred as vein type and cavity filling along the major fault zone or joint in granitic rocks e.g. Pai and Mae Sariang District, Mae Hong Son Provincerelated with Triassic granitic rocks (Department of Mineral Resource, 1985; 1986)

1.2.3 Western Granitic Belt

The Western Granitic Belt is largely Cretaceous age, I-type and S- type affinity. These granitiod rocks mainly distributed in Myanmar and cover small area in Thailand. In northern Thailand, the small isolated pluton is in Mae Lama, Mae Hong Son province (Charusiri et al., 1992). These rocks reflected true granite (Streckeisen, 1976) which medium-grained equigranular, grey, biotite-hornblende granite with some pyroxene and medium grained, grey, K-feldspar megacrystic biotite-hornblende granite (Cobbing et al., 1992). From 40Ar/39Ar yielded age 50- 88 Ma or Late Cretaceous to Early Tertiary (Charusiri et al., 1993) and from Rb- Sr whole rock isochron yielded ages 130.4±4.4 Ma (Nakapadungrat et al., 1984) at Mae Lama granite. Geochemically, these belts can be grouped into two groups (Cobbing, 2011), the Cretaceous granite S-types and I-types. The composition range from granodiorite to syenogranite dominated by monzogranites (69.0-74.4%

SiO2). They show strongly potassic with high K2O content that differ from the Permo-Triassic S-types granite which metaluminous subalkaline monzonitic to peraluminous alkali calcic granite. The Tertiary granites are metaluminous to mildly peraluminous I-type granitoid rocks.

1.3 The Doi Kio Lom (DKL) Area

The Doi Kio Lom (DKL) area locates in Pai district, Mae Hong Son province. (at 1,296 meter above mean sea level) This area is well known as a scenic area along border between Pai and Pang Ma Pha district. It appears on the topographic map: sheets 4647 I (Amphoe Pai), L7018 series, at scale of 1:50,000 at UTM 2150300N/428500E, and on the geologic map sheet NE 47-2 (Amphoe Chiang Dao) at scale of 1:250,000. Approximately at 19°26'45" latitude 98°19'8" longitude (Fig. 1.2)

Accessibility to the study area can be conveniently accessed by car via highway number

107 from Muang District to Mae Taeng District, Chiang Mai Province (approximately distance 37 kilometers). From Mae Taeng District turn left to Pai district, Mae Hong Son Province via the highway number 1095 that takes 90 kilometers far (Fig. 1.3)

Geological study of the DKL and vicinity areas were first explored by Department of Mineral Resources for mineral economic usage on 1:50,000 scale (Department of Mineral Resources, 1971). Then, the geological reconnaissance was surveyed by German Geological Mission in Thailand in cooperation with Geological Survey Division, Department of Mineral Resources. The geological map was published on scale of 1:250,000 (Hess and Koch, 1979). Consequently, geology mapping on 1:50,000 scale of Pai district was reported by Geological Survey Division, Department of Mineral Resources, Thailand (Department of Mineral Resources., 1985 (in Thai)). The results of the geological survey show that the study area displays variety of rock types. The pre- Tertiary rocks in this area composed of Cambrian to Triassic rocks (Hess and Koch, 1979). Sedimentary and metamorphic rocks in the Pai District are Cambrian to Permian in age. The Cambrian rocks are sandstone (orthoquartzite) and quartzite, light- to pale grey and green in color with fine to medium interlocking grain. Their texture exhibits banded and foliated texture that could be defined to quartz schist. Other metamorphic rocks are phyllite and quartzitic sandstone. The overlying rock unit is Ordovician limestone, these rock unit conformable overlain Cambrian rocks, constituted largely by limestone interbedded with argillaceous sedimentary rock. Other sedimentary rocks are made up of slate, black shale, calcareous shale, sandstone and chert. The Silurian-Devonian rocks are made up of sandstone and low-grade metamorphic rocks-phyllite, quartzite and schist, associated with granitic batholith as contact metamorphism (grade to slate or slaty shale). This rock unit is overlain by the Carboniferous sedimentary rocks, which consisted of sandstone, conglomerate, slate and chert. Volcanic rocks were founded as dykes across cut this rock unit. However, chert blocks in area of Carboniferous contain radiolaria aged Permian (Wonganan and Caridroit, 2006). Therefore this rock unit might be Permian rocks

Igneous rocks in the Pai District are plutonic rocks, occurred as batholith. Lithologically, the granitic rocks could be defined into 6 groups (Department of Mineral Resources, 1985), comprised of coarse-grained biotite granite, muscovite-biotite

granite, leucocratic granite, fine- to medium-grained granite, hornblende granite and syenite. This intrusive igneous batholith lies in nearly north-south direction. Rb/Sr age dating of rock samples collected from north and south east of Pai district gave Triassic age (Braun et al., 1976). Additional, Cretaceous alkaline complex is situated west of Pai district. The younger granitic rocks are a composite multiple intrusion of calc alkaline to subalkaline affinity. Lithologically, the rocks are syenites and quartz monzonites which flanked by biotite and hornblende-biotite granites.

Fig. 1.2 Geological map of the Doi Kio Lom area showing of distribution of rock units and accessibility (modified from topographic map sheet 4647I Amphoe Pai, L7018 series, at scale of 1:50,000 and geological map sheet NE 47-2 Amphoe Chiang Dao at scale of 1:250,000).

Fig. 1.3 Map of northern regions of Thailand showing accessibility to the study area (modified from Department of Highway, 2010).

1.4 Methodology

1.4.1 Petrographic Study

The standard thin sections (0.03 mm thick) of the selected samples were made and studied at the Department of Geological Sciences, Faculty of Science, Chiang Mai University. The thin sections were studied to characterize mineral compositions, textures and their alteration. To classify rock name based on their occurrences, textures and/or mineral constituents and geochemistry, also named the rock samples by using Streckeisen classification (1976). The results of petrographic study are summarized in Chapter 2 and individually reported in Appendix A.

1.4.2 Whole-rock chemical analyses

1) Powdered sample preparation

Powdered sample of whole rocks were prepared for all collected rock sample. These powdered samples were chemically analyzed in major oxides, trace elements, rare-earth elements (herein REE) and loss on ignition (LOI). The thirty selected rock samples were carefully prepared by cutting off the weathering surfaces of the least-altered samples, and then splitting into conveniently sized fragments and crushing into small chip (approximately 0.5 to 1.0 cm across) using Rocklabs Hydraulic Splitter and Jaw Crusher. Then, the rock chips were selected to avoid weathering surfaces, veins, xenoliths and were cleaned to make powder samples. The clean rock chips were divided by quartering into approximately 50-80 g. after that were pulverized by Rocklabs Tungsten Carbide Ring Mill to be powder samples. The powder samples were prepared at the Department of Geological Sciences, Chiang Mai University, Thailand.

2) Major oxides, trace elements and rare-earth elements

The chemical analysis of major oxides (wt%) (SiO2, TiO2, Al2O3, Fe total as

Fe2O3, MnO, MgO, CaO, Na2O, K2O and P2O5) were determined on fused

glass disks with 1:8 sample to Li2B407 flux ratio, using a Rigaku ZSX100e X-ray fluorescence spectrometer in the Key Laboratory of Isotope Geochronology and Geochemistry, the Guangzhou Institute of

Geochemistry, Chinese Academy Sciences (CAS), Tianhe, Guangzhou, Guangdong, China. The accuracy of the analyses is within 1% for most major elements. Additional, trace elements (Li, Be, Co, Cu, Zn, Ga, Mo, Cs, Ba, Rb, Sr, Y, Zr, Nb, Ni, Cr, V, Sc, Hf, W, Pb, Ta, Th and U) and REE (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) were determined on fifty-four carefully selected felsic to mafic volcanic/ hypabyssal rocks powder, using a Thermo Scientific XSERIES 2 Inductively Coupled Plasma Mass Spectrometry (herein ICP-MS) installed at the Key Laboratory of Isotope Geochronology and Geochemistry, the Guangzhou Institute of Geochemistry, Chinese Academy Sciences (CAS), Tianhe, Guangzhou, Guangdong, China. The ICP-MS analytical procedure is described in Qi et al. (2000). The analytical precision is better than 5% for elements > 10 ppm, less than 8% for those < 10 ppm, and about 10% for transition metals. Solutions for ICP-MS analysis were prepared with Qi et al. (2000) digestion technique. Analytical reagent-grade HF and HNO3 were used and purified prior to use by sub-boiling distillation. The screw- top PTFE Teflon Beaker bombs were cleaned using 20% HNO3 (v:v) heated to

100°C for 1 hour. Dissolution of igneous rock powdered samples were started with 35-45 mg of samples and weighed into 25 ml screw-top PTFE bomb. 0.6 ml (30 drops) HNO3 and HF (1:1, BVIII grade, Beijing Institute of Chemical Reagents) and 0.3 ml (15 drops) HClO4 (1:3) were slowly added to each sample bombs and were treated in an ultrasonic cleaner/bath for 60 minutes. Then bombs were placed on a hot plate with 100 °C for 48 hours, after that each bomb were opened, solution evaporated to dryness for remove most of silica. Next step, 0.8 ml (40 drops) HNO3 (1:1, BVIII grade, Beijing Institute of Chemical Reagents) were slowly added to each sample bombs and put on hot plate with 110 °C for 1 hour. After that 0.8 ml (40 drops) HF (1:1, BVIII grade, Beijing Institute of Chemical Reagents) and 0.3 ml (15 drops) HClO4 (1:3) were slowly added to each sample bombs. Then bombs were sealed and lined in stainless steel bombs (high pressure bomb). Next, they were placed in an electric oven and heated to

190°C for 48 hours. After cooling, the bombs were washed outside and opened before placed on hot plate with 150 °C for 12 hours (overnight) for evaporated to incipient dryness. The final digestion residue was re-dissolved by adding 4 ml 4NHNO3 to each bomb and closed. Resealed and lined in stainless steel bombs and returning them to the electric oven heated at 170 °C for a period of 4 hours. After cooling, the bombs were washed outside under and placed on the hot plate with 115 °C for 1 hour. The final solution was transferred into polypropylene bottles and weight for add 3% HNO3 2,000 time of sample weight. In addition, separate bulk sample aliquots were added 1 mgml-1 Rh and Re solution as an internal standard with 1:1 before ICP-MS analysis. The reagent blanks were treated exactly as were the samples.

In addition, separate bulk sample aliquots were leached with 2 M HCl and

0.5 M HNO3 for 24 hour under the room temperature to extract the leachable fraction. REEs in the leachable fraction were also analyzed by ICP-MS following a similar procedure as described above.

Analytical calibration was accomplished using aqueous standard solutions to correct for matrix effects and instrument drift. The standards used in ICP- MS analysis were the international standard (W-2, SY-4, GSR-1, GSR-2, GSR-3, BHVO-2, SARM-4, GDS-9 and AGV-2) and the internal standard (10 ppb Rh). The preparation for standards solution, Single-element 1000 mgl-1 stock solutions were prepared using pure metals or pure metal oxides. Four multi-element stock solutions were prepared, containing 10 mgl-1 of each analyze: (1) Li, Be, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Cs, Ba, Pb, Th, U; (2) Sc, Y and 14 REEs; (3) W, Mo; (4) Nb, Ta, Zr, Hf. The stock standard solution containing W and Mo was prepared in 2% NH3.H2O, whereas the stock standard solution containing Zr, Hf, Nb and Ta was prepared in 2% HNO3 and 0.2% HF. The multi-element working standard solutions were prepared (using the reagent blank solution as diluents) from the above mentioned stock solutions to span the concentration range from 10 to 100 mgl-1. At these concentration levels, all elements could be mixed

together. Working standard solutions were found to be stable over a period of 2 weeks. The detection limit for each element (in solution) was calculated as three times the S.D. of the ion counts obtained for the sample blank (measured for ten replicate determinations), divided by the sensitivity of 10 mgl-1 multi-element standard solutions. For Li, Be, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Zr, Mo, Cs, Ba, Pb the detection limit ranged from 0.01 to 0.2 mgl-1. For Y, Nb, Hf, Ta, W, Th, U and REE the detection limit ranged from 0.001 to 0.005 mgl-1. Detection limits for these elements in the solid (rock) can be estimated to be much higher that calculated for the sample blank, corresponding to the dilution factor used. The recoveries for most of these elements ranged from 90 to 110%. The result of sample analysis was illustrated in Chapter 3. Co result cannot reported in these studied because it may be contaminated with tungsten carbide ring mill.

3) Loss on Ignition determination (LOI)

Loss on Ignition was carried out at CAS by the gravimetric method, heating approximately 1.2 g. of each sample powder at 950 °C for 4 hours in felsic rock samples.

1.4.3 U-Pb zircon geochronology analysis

Three representative rocks were analyzed for Pb/Pb and U/Pb dating of zircon was conducted using LA-ICP-MS in the State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences.

Approximately 500 g of rock was repeatedly sieved and crushed in a Cr-steel ring mill to a grain size <400 micron. Zircon was separated using gravitation and magnetic techniques and then handpicked under a microscope in cross-polarised transmitted light. The selected zircon were mounted in 1 inch diameter epoxy resin block, ground down to expose their internal textures, and polished to obtain flat surfaces suitable for electron microanalysis. Sample mounts were coated with carbon and gold prior to electron microbeam and ion probe analyses, respectively.

Sample mounts were placed in a sample cell designed by Laurin Technic Pty. Ltd, flushed with Ar and He. Laser ablation was accomplished using a pulsed Resonetic 193 nm ArF excimer laser, operated at a constant energy of 80 mJ, with a repetition rate of 8 Hz and a spot diameter of 31 μm. The ablated aerosol was carried to an Agilent 7500a ICP-MS by He gas via a Squid system to smooth signals. Data were acquired for 30 s with the laser off, and 40 s with the laser on, giving approximate 100 mass scans. NIST SRM 610 glass and Temora zircon standards were used as external standards. Each block of 5 unknowns was bracketed by analyses of standards. Off-line inspection and integration of background and analysis signals, and time-drift correction and quantitative calibration for trace element analyses and U–Pb dating were performed using ICPMSDataCal (Liu et al., 2008). The age calculation and plotting of concordia diagrams was performed using Isoplot/Ex 3.0 (Ludwig, 2003). The detailed analytical technique was described by Li et al. (2006)

1.5 Thesis outline

The thesis divided into the five following chapters

Chapter 1 is an introduction and review of granitic rocks in northern Thailand, geology and their mineralization, study area and methodology used in this study

Chapter 2 presents lithology, petrography and their alteration of the granitic rocks from the DKL area.

Chapter 3 presents geochemical data of the granitic rocks from the study areas, include elements mobility, tectonic discrimination diagram and U-Pb zircon age dating.

Chapter 4 discusses fluorite mineralization and alteration

Chapter 5 conclusion and discussion about mineralization related to petrology and tectonic setting of igneous rocks in the Doi Kio Lom area.