Geosciences Research

7

Authors: P K Yadav

In the recently drilled deeper boreholes by HZL new intersection of lead and zinc ores have established depth ward continuity of ores of previous boreholes and have thus augmented reserves considerably. It has suggested revision of ore forming concepts and also that in the Rajpur Dariba area further search for Zn-Pb should be carried out using new innovative techniques. Success often requires supplementing standard procedures with the effective use of new exploration methods: the kind that can see deeper, are more definitive, and more efficient to ore discovery. The conventional methods have their place, but these are proving to be less effective as new terrains are increasingly more difficult to explore. Present studies have helped in searching new controls of mineralisation and in formulation of new ore guides for future search of new ore bodies. On the basis of present studies like facies of volcano-sedimentary sequence, textures, structures, ore microscopy, environment of ore deposition, characters of mineralisation, ore facies, sequence stratigraphy, airborne and ground geophysics new evidences for ore genesis have been collected. In Sindesar Khurd these studies have suggested vent complex type of hydrothermal sedex deposit. Rajpura Dariba deposit displays biphase mineralisation including stratiform sulphides and post metamorphic epigenitacally melt introduced independently. Salient features of vein ores such as occurrences as pods, segregation veins or open space fillings traversing the banded ores, absence of deformation and recrystalisation textures indicate that these veins are post-metamorphic and could have formed from a different ore fluid. The cavity filling nature of vein ore and their occurrence in irregular shear planes suggest their environment of ore formation was different than imprints of metamorphism in banded ores. The source of this fluid could be intrusive granite located during present studies. Now with an objective of searching new ore zones more evidences like faults and shear zones which are loci for ore in volcanoclastic rocks and calc silicate marble is the best host. Other evidences of ore forming processes and characters of volcanic rocks are also helpful in ore search. These strategies are discussed in this paper to search new local targets for selecting new drill sites.

13

Authors: V.A. Guryanov, A. Yu. Peskov

This paper attempts to summarize and systematize findings of geological, geophysical, geochronological and geochemical studies over the past three decades on Late Paleoproterozoic granitoids, basites and sedimentary-volcanic rocks of the Ulkan trough in the southeastern flanking of the Siberian Platform, which make it possible to identify their sources and to reconstruct conditions and geodynamic settings of their formation. Rocks of the Ulkan volcano-plutonic complex are found to form in an anorogenic environment under intra-continental extension in relation to the mantle plume activity at 1.77 – 1.70 Ga. Based on geodynamic criteria, five stages recognised in the evolution of the Ulkan paleorift system can be grouped into three major stages of the Late Paleoproterozoic intra-plate magmatism. The study of data made it apparent that the Ulkan paleorift system has characteristics of a three-armed structure indicative of the intense rifting in response to the hot spot activity; the Ulkan alkaline-granitic batholith with its distinct metallogenic specialization for rare-earth elements (REE) and rare earth metals (REM) could be such a hotspot-type diapir. Tectonically, the triple junction appears as a zone that underwent intense intra-plate alkaline-granitic magmatism in the Late Paleoproterozoic and hosts ore targets unique in scale and diversity (Be, Ta, Nb, TR, Zr, U, Au, Li, Sn, Mo, P, and Ti) with ages in the 1.72 – 1.67 Ga range. Rare-metal and REE deposits are essentially the product of rare-metal alkaline granitic magmatism and most likely related to the evolution of the mantle source in the course of plume activity. The presence of both subalkaline granitoids and volcanic rocks (K-series) and alkaline granites, comendites and pantellerites (Na-series) intensely fractionated and enriched to a maximum degree in most noncoherent elements, as well as Zr, Mn, F, Fe, Ti, is characteristic of the Ulkan anorogenic magmatism. Granitoids of the Ulkan paleorift structure and its southern flanking foldbelts have mixed mantle-crustal sources. Subalkaline granites are derived from a source containing material from lower continental crust and alkaline granites from a mantle source containing the OIB-type component. The origin of the Ulkan-Bilyakchan volcano-plutonic belt initiated as an intracontinental system along the southeastern edge of the Siberian Platform is considered to be related to hot spots of this type.

21

Authors: Risto J. Pirjola, David H. Boteler

To assess the geomagnetic hazard to power systems, it is necessary to model the Geomagnetically Induced Currents (GIC) produced during space weather storms. This requires knowledge of the geoelectric fields that drive GIC. In the time domain, the geoelectric fields can be calculated using a convolution integral including the geomagnetic field or its time derivative and an impulse response function for the Earth. In principle, the integral extends to infinity but for practical calculations the impulse responses must be truncated at a finite length. In this paper, we investigate the effects of the truncation on the calculation of the geoelectric fields. We consider how long the impulse responses need to be to obtain sufficiently accurate geoelectric field values. It is found that the high-pass impulse response used with geomagnetic data can be truncated very early, e.g. at 1 h, while the low-pass impulse response used with geomagnetic time derivative data must be extended much longer, e.g. until 24 h.