The present paper is written to bring to light a dichotomy that is noted in a naturally deformed rock, where the sense of shear inferred from quartz shape preferred orientation (SPO) is opposite to that deciphered from the crystallographic preferred orientation (CPO). Microstructural and quartz CPO data (obtained through SEM-EBSD analysis) from a quartz vein hosted in sinistrally sheared mylonitized granite of Gadwal region (Dharwar Craton) are presented. The vein thin section is prepared parallel to the kinematic reference frame (XZ section of the strain ellipsoid) using field-based information, which allows determination of sense of shear using microstructures. Three domains viz. Domain-I, II and III are identified in the rock thin section with grain size being 300-180 µm, 70-35 µm, and <20 µm, respectively. Of these, quartz grains of Domain-II show a well-defined quartz oblique grain shape fabric, which is indicative of dextral sense of shear. However, quartz CPO from the same Domain-II, as well as Domains-I and III, consistently shows a sinistral sense of shear; the latter complements the kinematics noted from the host rock mylonite. The dichotomy noted from Domain-II indicates that there maybe pitfalls in direct interpretation of kinematics based exclusively on quartz SPO analysis. Hence, caution must be exercised while extrapolating microscale kinematics based on quartz SPO to the regional scale.
<p>Hydrothermal veins can form when pre-existing anisotropy gets dilated by increase in fluid pressure (P<sub>f</sub>). In addition fluctuation in P<sub>f</sub> can result in the deposition of economically important deposits, such as gold in veins. Therefore, statistical analysis of dilational quartz veins can help to identify the mineralization potential of an area. This present study is focused on this aspect. The metavolcanic rocks of Dharwar Craton (Southern India) are replete with quartz veins, but mineralization is restricted to certain domains in the vicinity of Gadag, Hutti, and Kolar. To study the topological importance in mineral exploration, an experiment is carried out in different parts (e.g., Gadag, Hutti, Raichur, Gadwal) of Dharwar Craton. Orientation of dilational quartz veins, thickness, and spacing data are collected from different transects of the above-mentioned areas. Variations in driving pressure ratio (&#916;R&#697;), fractal dimension (Dc), Weibull modulus (&#945;), vein intensity (Vi), and coefficient of vein spacing (C<sub>v(S)</sub>) are calculated from vein data of each transect. These parameters are integrated to plot a three-axes &#8220;mineralization potential plot&#8221;, also known as P-D-F plot (Lahiri et al., 2020). The distance between the origin (0,0,0) and the point representing the transect in the P-D-F plot gives the &#8220;mineralization potential parameter&#8221; (Md). It is established that a transect in mineralized zone is represented by a point that lies closer to origin than non-mineralized zone. However, it is our observation that the points representing mineralized zone show more clustering on the P-D-F plot, whereas the points representing non-mineralized zone are dispersed. &#160;We infer that in order to identify a zone as having high mineralization potential, the Md value should not only be lower but also the clustering should be higher.</p>
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