Análise geoestatística das fraturas e lineamentos e suas implicações nas ocorrências de depósitos minerais na região de Santa Luzia-PB.

Abstract

This dissertation deals with the extraction and geostatistical analysis of the linear geological features such as fractures and lineaments with the objective of its application in spatial variability and in mineral exploration in the region of Santa Luzia-PB. The study area is located in the micro region of Alto Piranha Depression in the central part of the arid region in the Northeast Brazil. This region is part of the Geological Province of Borborema located between two fault systems (mega zone of Brazilian fault systems), characterized by Patos Lineament with ductile deformation with transcurrent dextral in nature in which occur Group Serido which is known for the mineral deposits of copper, gold, molybdenum, nickel, tungsten, scheelite, barite, iron, titanium, vermiculite, limestone, talc e minerals of pegmatites apparently controlled by fractures and faults. Linear structures were extracted from the fracture and lineament maps of 1:100,000 and utilized georeference variable of azimuths and through a FORTRAN program an ASCII file was created to analyze with GEO-EAS. A total of 1,174 fracture traces was extracted and the mean azimuth of fractures was 139,07° with a standard deviation of 21.26, showing a relatively small dispersion in the strike. The coefficient of variation of 21.04% is relatively low, indicating minimum variation in the fracture azimuths and showing a skewed distribution. The nature of the distribution of the azimuths tend to be multimodal with the modes in 104°, 140° and 180° respectively. Lithologically the fractures show ruptile nature with principal strikes varying from N-S/N30W, N30-60W, N70/E-W. The N-S/N30E fractures coincide with the lineament directions. A total of 2,160 lineaments azimuths were extracted and the mean direction obtained is 235.11° with a variance of 1,280.11 which is relatively high. The variation tends to be low with coefficient of variation of 15.22%. The nature of the distribution of lineaments is apparently unimodal with maximum frequency at 220° in the northern region and 275° in the southern region of the study area. The lineaments are of ductile in nature with foliation in E-W or in NE direction. Principal structure is Patos lineament zone with E-W strike with dextral movement of strike-dip-slip type. Based on the structural pattern analysis it could be noted that the mineral deposits are tend to be related to geological structures and majority of the deposits occur with in the mylonitic zone as fracture fillings. Geostatistical analysis was made of the fracture and lineament azimuths which were grouped into small groups for a detailed variographic analysis. The experimental variograms elaborated are robust and show well defined variographic structures. The variograms show some proportionality factor and are isotropic in nature with sample range of 25 km for fractures and 9.5 to 10.5 km for lineaments. The variograms show hole effect and nugget variance, which is caused by the presence of fractures of various tectonic events in the study area. Variogram models obtained in this study show the influence of cronological structural evolution in the region.