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Quartz Vein Exploration by 2D Resistivity Imaging

Application of 2D Resistivity Imaging —— Quartz Vein 


Quartz mineral currently plays as a role of strategy mineral in Thailand which may exploit quartz as a raw material for producing solar cell. High potential of quartz deposit zone is widely found at the Western part of Thailand; Ratchaburi and Kanchanaburi province where contain various quartz mines and two quartz purified factories. 2D resistivity imaging technique with automatic measuring by multi-electrode (60 electrodes) system and designing 10 m electrode spacing for target depth of about 100 m, was successfully applied to located subsurface quartz vein deposit and geological structure involving quartz occurrence at operating quartz mine zones. Technically, Dipole-Dipole and Schlumberger configurations were designed for obtaining detailed 2D inversion models. Quartz vein dimension could be identified with a conceptual interpretation of high resistivity contrast of quartz vein (presenting as high resistive value > 500 ?m) and a lower resistivity (< 100 ?m) of surrounding sediments and country rocks (e.g. sandstone, shale, and mudstone etc.). New quartz deposit zones located at the Northern area of an existing quartz potential zone, (Nongprue district) were identified by 2D resistivityimaging measurement. As a result of subsurface quartz vein dimension mapping, high intensive quartz deposit area was found covering the prospecting area of 2 km x 3 km. The assessment of ore reserve from only one quartz vein whichestimated as the width of 20m-40m, thickness of 20m to > 30m and extended length of 200m to > 300m (longest one is 600 m long), is >1 million tons. The quality of these quartz zones (taken from > 10 samples) is found as a high grade type (SiO 2 >99.5%) which is highly needed for the quartz factories. An achievement of 2D  resistivity imaging to figure subsurface quartz vein deposit, presents a high grade and potential quartz area at new potential zone, Nongprue district, Kanchanaburi province of Thailand.


Quartz is recently achieved by attracted quartz mining due to enhancing alternative energy that quartz can be utilized as a raw material for producing solar cell. Quartz potential in Thailand can be identified at several province,


The aims of 2D resistivity measurements are to determine subsurface geological structures and quartz deposit zone. The result may be presenting as geo-electrical cross-section in 2D models which may indicate for location of quartz deposit zones and loose quartz boundary for shallow quartz zone. Geological structure that may concern with quartz occurrences which may help to understand geological ore deposit.


3.1 Lacation

The survey area is situated about 1.5 km, South of Nongprue  town,  Nongprue  district,  Kanchanaburi Province, Thailand and about 80 km north of Kanchanaburi city covering the area of 2 km x 3 km (see Figure 1). Topography at the survey area is partly hilly mountain at the North of survey area surrounded flat area with elevation of 135 m (at flat area) to 260 m (at Northern mountain zone) above mean sea level. Land use at surround survey area is mostly planting sugar cane and tapioca.


Figure 1. Location of the survey area of Nongprue quartz zone.

3.2 Geology
Partly geology of Kanchanaburi province is found as composed rocks from Precambrian Era to Quaternary sediment. As seen from geologic map around the survey region in Figure 2, the survey area is situated in Silurian-Devonian-Carboniferous rocks which composed of black shale, chert, and siltstone, calcareous limestone and partly zone is covered by colluvial and residual deposits:gravel, sand, silt, laterite, and rock fragments of Quaternary sediment. Ordovician rocks (composed of argillaceous limestone and limestone, gray and pink; dolomitic  limestone  and  schistose  marble;  with interbedded shale, calcareous, and sandy; shale) is found at the Southern and Western region of the survey area. Triassic granite exposes mainly at the south-west of the survey area which composed of biotite granite,tourmaline  granite,  granodiorite,  biotite-muscovite granite, muscovite-tourmaline granite, and biotite-tourmaline granite Quartz deposits at the survey area are generally found at slightly undulating terrace with 1-5 m wide outcrop (see Figure 3).


Figure 2. Geology of the survey area.                                     

Figure 3 Quartz outcrop is extensively found at the Northen up-hill part of the survey area.

4.1 Resistivity measurements
Resistivity reading is represented by an apparent resistivity, a which can be calculated from observed potential value, V, injected current, I and geometric factor of the electrode configuration.The current is injected into the ground by current electrodes (C A , C B ) and the potential change in underground can be detected by potential electrode (P M , P N ). (Telford et al.,1990).

Figure.4 General resistivity array positioning current electrode CA-CB and voltage probes PM-PN.

Figure. 5 Pattern of current movement in subsurface of Dipole-Dipole array used in 2D inaging measurement.

4.2 2D resistivity imaging technique
Automatic resistivity reading with 60 multi-electrode was applied which obtain a pseudo-section over a horizontal distance of about 600 meters Electrode configuration were designed Dipole-Dipole array.(depth of >60 m). Resolution of measuring technique is 10 m due to reading station spacing of 10 m. To increase depth of investigation, reading stations was enhanced to 20, 30 and 40 m. with 10 m moving forward for one spread measurement. (explained in Figure 6).


Figure.6 Automatic reading with 60 multi-electrode technique to obtain inversion model presenting as 2D geo-electrical section                

Figure 7  Setting up 2D resistivity imaging instrument at the southern of the survey area and quartz vein deposit widely found.

Normally, quartz vein (zone) produce moderate to high resistivity which is clearly classified quartz zone from country rock. By interpretation concept, quartz vein should appear as vertical dyke form which responses as very high resistivity comparing to subsurface geological environments such as topsoil, weathered rocks or sediments.Interpretation of 2D resistivity cross sections and resistivity mapping at different depth can be identified as follows;
1. Possible thick quartz veins (QTZ) (high resistivity zone > 500 ?m in red color) appearing at depth of more than 10m (?12-25m) and vary width (10-50m). The thickness of quartz vein is found as 20 m to
more than 50m.
2. Surface loose quartz (LQ) is generally found in the survey area presenting as shallow high resistivitywith vary thickness (less than 10m) except where QTZ is found.
3. Fault and contact zone (F) could be drawn in 2 directions i.e. NW-SE (main fault direction) and NE-SW. From 2D inversion model, quartz veins mainly appear as 40m thick and 25 m. Some quartz zones expand to deeper > 50m thick. Figure 7 is an example of a typically resistivity section that quart was achieved to map quartz vein in this area. 2D resistivity imaging is achieved in many survey line at the uphill north part in both north-south and east-west direction which quartz veins can be presented as high resistivity zone (Figure 8) with trend mainly in NW-SE. Quartz veins can be mapped (as seen resistivity map at depth of 30 m, Figure 9) show a main quartz vein trend in NW-SE with > 600 m long. Quality of quartz in the study area is 99.4-99.6 percent where LOI is about 0.34-0.45 percent. (seen in Table 1) Quartz vein zones were further explored by 2D resistivity imaging at the southern part of the survey area. Quartz vein deposits are widely found with its dimension of 15-30 m width and 20 m-40 m thickness. (seen in Figure 10).


Figure 8 Interpreted geo-electrical section in N-S and E-W direction at the northern part of the survey area.Red color zone may presentsv as quartz zone.

Figure 9 Resistivity map (at depth of 30 m) presents high resistivity zones (red color) interpreted as quartz vein deposit zones,trend mainly in NW-SE.



Table 1. Example of chemical analysis result of some quartz sample showing high grade of quartz deposits in this area.

Figure 10. Several major quartz vein deposits are found at the southern portion of the survey area by interpreted resistivity cross-section of both south and eastwest directiom presenting quartz vein (red color)in 3D view.

In conclusion, 2D resistivity imaging technique has been applied as an effective way to pinpoint the quartz vein deposit zone as very high resistivity value that clearly identified by contrast of resistivity value. It is proved that High potential of quartz deposit is covered 6 km 2  with high grade quality.