A OPEN PIT MINING AÇIK OCAK MADENCİLİĞİ

analisys degradation and erosion risk
mapping in a GIS environment, but also the
evolution of degradation of landforms.
The successfull applications of unmanned
aerial vehicle (UAV) in the field of closerange
photogrammetry (Neitzel et al. 2011)
on abandoned mine areas have encouraged
the development of new methods for rapid
low-altitude image survey (from a few
meters to a max. of 80 meters of altitude).
With a GPS basis grid, acquired with
accuracy below the meter, the UAV
photogrammetry platform equipped with
SLR high-resolution digital camera is
capable of performing a very accurate
photogrammetric data acquisition.
However, this accuracy is not sufficient
for the geoprocessing computations that
need, besides the GPS flight log, the
acquisition of ground planimetric and
altimetric ground control points (GCP)
coordinates using a real-time kinematic GPS
(RTK-GPS).
The processing of aerial photographs was
performed with the PhotoScan software
(AgiSoft LLC), particularly suitable for
photogrammetric survey of morphologically
complex surfaces (Verhoeven 2011).
The photogrammetric method proposed
in this work is based on several missions
(flight and data acquisition) planned in the
lab with dedicated software, starting from
the area of interest (AOI) and the required
ground sample distance (GSD), knowing the
parameters of the digital camera. The
photogrammetric acquisitions was performed
both by horizontal and vertical planes data
acquisition, needed to the generation of
orthophotos, DEMs and 3D objects.
2 STUDY AREA AND GEOLOGICAL
SETTING
The studied area covers about one square
km near the Monte Porceddu, between the
basins of Rio S'Alluminu and Rio Maccioni.
This abandoned mining area offers wide
artificial landscape landforms that show
several geometrical complexities (Fig. 1). It
is characterized by several quarries with high
vertical wall, stratified with layers affected
by hydrothermal and intermediate to
advanced argillic alteration and
silicification.
This study if focused, at the moment, on
the northern area of the Monte Porceddu
mine (AOI, Fig. 2), where the argillic
alteration is characterized by kaolinite and
dickite as main minerals, accompanied by
quartz, pyrite and pyrophyllite. This
alteration involves the complete
transformation of the pre-existing andesitic
rock, with obliteration of the particular
former textures.
The ore grade kaolin occurrences coincide
with areas where the advanced argillic
alteration reached a pervasive level: this
happened especially where the original rocks
were very permeable, thus exposed to
etching by acid solutions. The kaolinized
bodies have been no longer exploited
because of low quality of the ore which is
too rich in silica and pyrite. The silicification
type is due to deposition of mobilized silica,
both as impregnation of volcanic and
volcano-sedimentary rocks and as crusts. In
fact, a broadly tabular, flat-lying crops on
the top of Monte Porceddu overlies the
kaolinized area. This silica body is
characterized by the occurrence of
chalcedony and small shallow-seated
eruption breccias. All these features suggest
that this may be a silica cup, formed in the
surficial part of the epithermal system, above
the water table, by acidic and relatively cool
steam-heated fluids. The silicification
alteration occurs also at the contacts between
andesitic domes and the epiclasticpyroclastics
units. Within the latter, the
intensity of silicification is also controlled
by the permeability of the layers. The
distribution of silicic alteration suggests that
hydrothermal fluid flows channeled
preferentially along lithological contacts.
A complete understanding of the
geological structures in relationship with
degradation landforms, derived by past
mining activities, is the most important
factor to define the different consistent
resolution of DEMs and the appropriate
scale for planning the photogrammetric
survey of this area.
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