COSTA FILHO, A.; http://lattes.cnpq.br/0713096121337436; COSTA FILHO, Antonio.
Résumé:
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.
