The purpose of this study is to undertake field visit to dimension stone (Dolerite Dykes, Market name “Black Granite”) deposit and quarry in Namal Khatha, Oghi, Mansehra, Higher Himalayas of north Pakistan, and to undertake assessment for technological up-gradation and model quarry development project for mechanized quarrying of dimension stone. The area is currently being mined by Indus Mining for the last decade, but there is no feasibility or reserve estimate report available. The area is located about 48 Km from Mansehra on Oghi-Darband Road. Mine is reachable through a jeep-able road from Namal Khatha. In past, various consultant geologists the study area but there is no detail geological assessment report available for this economic deposit. The main objectives of the present study are to review of the studies done by the local engineers and selection of the most significant areas for model quarry/up gradation and to estimate the remaining reserves of the dolerite (Black Granite). Two investigations methodologies were adopted in order to achieve the desirable projects objectives.
Key Objectives
Key objectives of the present investigation were;
1. To map the joints and faults and integrate the dataset with geophysical data to provide
direction and to estimate the remaining reserves of dolerite (Black Granite)
2. To suggest suitable location & direction for future mining in the studied area.
Resistivity imaging equipment
The apparent resistivity data is recorded by using low frequency alternating and direct current. the Geomative GD-10 (Resistivity Meter /IP) was utilized to acquire electrical resistivity data in the research area. This equipment is commonly used for groundwater exploration, environmental and engineeringews and geological investigations etc. it is light in weight, convenient in operation, having transmitter and receiver are combined in the same case. It can perform both resistivity and induced polarization measurement simultaneously, this equipment can be used to acquire multi electrode resistivity measurement. The nine configurations of electrodes are displayed by large LCD. Other main accessories of the equipment are 300 m long multi electrode intelligent cable with 5 m takeout spacing, four rechargeable batteries, 60 stainless steel electrodes, hammers and measuring tapes. However, in this research only 60 electrodes with 1, 2 and 3 m electrode spacing were used (due to topographic constraints) to image the internal structure of the landslide. The Geomative GD-10 resistivity / IP meter is designed for optimum versatility in infrastructure projects and environmental studies. Additionally, the tool has built-in quality control and feedback to operator. It can acquire 1D, 2D and 3D and 4D geo electrical resistivity surveys.
Electrical resistivity tomography field data acquisition and processing
In the current research project, Geomative GD-10 (Resistivity / IP) meter has been used for acquiring ERT data set by implementing various electrodes configurations such as Dipole dipole, Wenner and Schlumberger, in order to get detailed scanning of the subsurface anomalous zones and geological structures.
This kind of approaches have provided fruitful information for interpreter and helpful in understanding the near surface phenomenon. Furthermore, ERT profiles using 1, 2 and 3 m electrode spacing in order to obtain a reasonable resolution, reliable subsur
ERT Profile 01
Electrical resistivity variation show low and high zones are present in the inverted ERT images and manifest the fissured zone geometry and its orientation. In electrical resistivity investigations, the instrument measure the potential difference of voltage injected into heterogenous and anisotropic subsurface, the apparent resistivity data need to be inverted to true formation resistivity in order to reconstruct the subsurface resistivity of the underlaying strata. It is essential to apply proper inversion technique and aid to generate ERT imaging profiles for interpreting the subsurface. The subsurface concur the abrupt drops in electrical resistivity indicate the highly fractured zone (high water content) or probably higher clay/water contact or mineralogical composition. These zones are usually related to the internal structure of subsurfacestrata. ERT Profile 1 was acquired in as shown (Fig1). Inverted section ERT Profile 1 indicates different layering and contrasts in electrical resistivity along the acquired section. A semi-continuous very resistive layer is located near the urface having variable thickness and ranging in resistivity between (3000 to 10000 Ωm), which depicts the partly fissured zone of the parent rock (Dolerite). The first 14 meter horizontal distance approximately along the profile up to the depth of 8 meter can provide good yield. Contrary, lower resistive layer appears beneath the toward end of the profile is high fissured zone, from top of bottom 2 meters with resistivity ranging from (15-560 Ωm). The high-water content in the fractured in dolerite and gouge material creates the higher conductive / low resistive alues. Additionally, this zone is continuously propagating down the depth
Figure 2. illustrate the various fissured zone based on electrical resistivity contrast values
ERT profile 02
Inverted section ERT Profile 02 indicates different layering and contrasts in electrical resistivity along the acquired section. The first 48 meter is in the contact point of dolerite & the host rock,the (48-78-meter) horizontal distance highly fractured zone is located up to the depth of 18-20 meter. 78-96 meters partly fissured zone is located and can provide good quality of dimension stone in the studied area. From 96-174 meters, the first 18-22 meter is highly fractured zone, however, the deep zone below (22 meter) indicated moderate fissured zone.
Figure 3. shows the resistivity variation of surface soil, contact points and dolerite fissured zone
ERT profile 03
Inverted section ERT Profile 03 indicates different layering and contrasts in electrical resistivity along the acquired section. The first 48 meter is in the contact point of dolerite & the host rock,the (48-58-meter) horizontal distance highly fractured zone is located up to the depth of surface to 12-meter depth. 58-174 meters horizontal distance indicates highly fissured zone and the its extended up to the depth of 12-18 meter. Which cannot provide good quality of dimension stonein the studied area. However, the deep portion below (12-18 meter) are moderate fissured zone, and its extended up to the depth of 36-meter depth
Figure 4. shows the resistivity variation saprolite, contact points and dolerite fissured zone
ERT profile 04
Inverted section ERT Profile 04 indicates different layering and contrasts in electrical resistivity along the acquired section. The near surface is comprised of Saprolite, however, can spot good quality between 40-64 meters horizontal distance. The 8-12 meters depth zone along the profile is comprised of highly fractured zone. The lower portion from 32-96-meter horizontal distance at depth below 12 meters provide moderate fissured zone and can provide better yield. Additionally, this zone is extended up to the depth of 24 meter. 58-174 meters horizontal distance indicates highly fissured zone and the it is extended up to the depth of 12-18 meter. Which cannot provide good quality of dimension stone in the studied area. however, the deep portion below (12-18 meter) are moderate fissured zone, and its extended upto the depth of 36 meters depth
Figure 5. shows the saprolite, moderate & highly fissured dolerite zone
The surface geological and geophysical techniques were combined in order to map the intrusive bodies for development of commercial quarry. The dolerite was estimated using electricalresistivity, depth, width, length and specific gravity value. The target rock was distinguished from other associated rocks using resistivity variation. It is suggested to start development in the green zone for successful project outcome.
Industry-leading geophysical equipments and service provider supplier
