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Abstract: This research intends to use the ultrasonic properties of the rocks to classify weathering grade of sandstones and to correlate their physical and mechanical properties. Sandstone specimens were collected from Nam Phong (NP) and Phra Wihan (PW) Formations, Khorat Group, Northeast Thailand. Three weathering grades were categorized as fresh (I), slightly weathered (II) and moderately weathered (III). Petrofabric of both NP and PW sandstones at each degree of weathering were observed. Physical properties and uniaxial compressive strength tests were also conducted in the laboratory. Both ultrasonic compressional (Vp) and shear (Vs) wave velocities of the rocks were measured. The results of the research indicated that the ultrasonic wave velocities decrease as increasing of degree of weathering and porosity. On the contrary, the wave velocities increase as increasing percentage of quartz, density and uniaxial compressive strength. 1 Introduction The strength and other engineering properties of rock materials were usually reduced when the rocks are weathered. In generally, weathering is the process which changes the properties of rock mass due to changing the environment conditions such as physical, chemical and biological. Khorat Group, the non-marine red-beds sandstone, forms mostly in the Khorat Plateau, Northeast Thailand which is in tropical area (Figure 1). Sandstone is a sedimentary rock that composed of sand-sized grains of mineral, rock fragments, or organic material. It also contains the most common cementing materials that are silica and calcium carbonate; accordingly, it is very moisture-sensitive and easily weathered due to reaction with water. Thus, the authors interested in weathered sandstone of the Khorat Group. This Group was named by Ward & Bunnag (1964) who subdivided the group into 9 Formations, namely from older to younger sequences (Triassic to Cretaceous) as, Haui Hin Lat, Nam Phong, Phu Kradung, Phra Wihan, Sao Khua, Phu Phan, Khok Kruat, Mahasarakarm and Phu Thok Formations. The rock samples in this research were taken from Nam Phong and Phra Wihan Formations that Nam Phong Formation deposits in Triassic and Phra Wihan Formation deposits in Cretaceous. The Nam Phong Formation has a type section along the Nam Phong stream and distributes along with the Loei-Phetchabun Fold Belt and the western regime of the Khorat Plateau. The formation consists of resistant red-brown micaceous sandstone, siltstones, mudstones, and conglomerates of fluvi-atile origin (Chonglakmani 2011). The Phra Wihan Formation is widely distributed, occurring in the Phu Phan Rang and around the western and particularly the southern rims of the Khorat Plateau. Generally, the rock consists of light buff to gray, fine to coarsegrained quartzitic sandstones and rare siltstones and mudstones with occasional conglomerates (Meesook 2011).
ABSTRACT Chatree Gold Mine is the largest open pit mine in Central Thailand which produced 74,137 ounces of gold in July 2007 – June 2008. The Chatree deposits consist of complex andesitic centers adjacent to the rhyolitic centers. Structural geological of interested area (CH pit) can be divided in to 3 main structures: sheared zone, andesite dykes and faults. The point discussed in this paper is general production blasting practice and controlled in 6 meters bench using three main blast patterns with powder factor between 0.35 and 0.80 correlated to rock type. Trim blasting and pre-split blasting have been proposed, trialed are also include. The present practices are mentioned. 1 INTRODUCTION 1.1 Background The Chatree Gold Mine is located 300km north of Bangkok in Thailand. The Chatree deposit was discovered in 1995 in an area not previously recognized as having potential for significant gold mineralization. Mining leases were applied for and granted in 2000 and Chatree North Project mining leases were granted in 2008. The Chatree Gold Mine commenced production in November 2001 after a 12 month construction period. Load and haul is done using a fleet comprising of O&K RH40E excavators, Cat 773 and 740 trucks, Cat 14M Grader and Cat D8 and D9 Dozers. Mining and haulage are done by local Thai contractor, Lotus Hall Mining. This contract was updated in 2007 to allow for a new and expanded mining fleet, supported by Caterpillar, for increased production at Chatree for the year ended 30 June 2008 was 74,137 ounces of gold and 232,039 ounces of silver. The mine is conventional open pit operation consisting of three currently operating mine areas (A,K east and C cutback) and six closed pits (p, CH,H west, H south, D and S). the mine area spans approximately 7.5 km by 205 km and the deepest pit wall is 153 meters from surface (Plate 1). (Plate in full paper) The slope angle is designed correlated to rock types, which are 35The slope angle is designed correlated to rock types, which are 35 in laterite layers, 45 – 50 in transitional rock and sheared rock, and 60- 65 in fresh rock. Catch benches of 5–6 meters are introduced every 18 meters bench height. Blasting is done every 6 meters for two excavation flitches of 3 meters. This paper detailed the procedures and practices that have been developed for a production blasting and anear-wall blasting in Chatree Gold Mine closed and currently operating pits. 1.2 Geology The Chatree deposits are located in the Western-Edge Khorat Plateau Gold Belt at the boundary of Phichit and Phetchabun Provinces, central Thailand. The deposits consist of complex andesitic centers interdigitate and are overlain by fine-grained volcaniclastics and epiclastic siltstones, mudstones and fossiliferous limestones. Instructions of diorite to dolerite occur in the region. There are also stocks and swarms of ddykes and faults in the area and granitic intrusions are associated with regional structural trends. While CH pit is dominantly composed of lithic rich fiamme breccias, polymitic and andesite to andesite porphyry.