Page 315 - Introduction to Mineral Exploration

298 M.K.G. WHATELEY

the hole. The sonic log is also used in estimat- westerly strike-slip movement of the west
ing the rock quality (fracture frequency), and Anatolian Extensional Province took place. At
the dip meter can be used to interpret sedi- the same time a series of NE-trending grabens,
mentary structures (Selley 1989). such as the Soma Graben, began to form in
A geophysical log showing the typical re- western Turkey. These grabens began to fill
sponses that the rocks in the Soma basin give, with Serravallian (Samartian) sediments, which
is described in section 13.3.2. contain thick lignite deposits.

13.2.4 Sampling 13.3.2 Geology of the Soma Basin
It is essential to establish a procedure for The Soma Basin contains thick deposits of
sampling core and working faces so that conti- Miocene and Pliocene sediments (Fig. 13.3),
nuity is maintained throughout an exploration which range in age from Serravallian
project and into the mining phase. For example, (Samartian) to Pontian (Gökçen 1982), but do
at Soma the whole lignite sequence was not contain volcanic rocks. The Tertiary
sampled, including all parting material. The sediments rest unconformably on Mesozoic
core was split and one half was retained in basement rocks. The stratigraphy of the basin
the field. All lithological layers in the seam is summarized in Fig. 13.4. It contains two
greater than 30 cm thick were sampled. Thin- thick Miocene lignite seams designated the
ner layers were included with adjacent layers KM2 and KM3, but this case history deals only
until a minimum thickness of 30 cm was with the KM2 seam.
obtained. The 30 cm limit was used as it was The Mesozoic basement forms rugged topo-
considered by the study team that this was the graphy around the basin of limestone hills
minimum thickness of parting that could be rising to 350 m above the Tertiary sediments.
mined as waste in the open pit (see also Boreholes which reached the basement con-
sections 13.6.1 to 13.6.3). This ensured that firmed the presence of limestone below the
weighted average estimates for run-of-mine sediments in the basin. At Soma, the top of
(ROM) lignite could be made. the basement appears to consist of debris flow
deposits.
The Miocene deposits have been divided into
13.2.5 Grouting
three formations (Fig. 13.4). The basal Turgut
Where deep coal is likely to be mined by under- Formation is predominantly immature sand-
ground methods, all holes drilled prior to min- stone and conglomerate, but there is a grada-
ing should be sealed using pressure grouting. tional upward fining of the sediments to the
This will reduce the potential water inrush lignite horizon. Increasing amounts of sandy
hazard in underground mining. clay, clayey silt, and carbonaceous clay appear
towards the top of the formation until these
grade into the KM2 seam. The basal contact of
13.3 GEOLOGY the seam is gradational and is usually placed
where the first recognizable lignite appears
with less than 55% ash content. The lignite is
13.3.1 Geological setting
hard, black, and bright, has numerous cleats
The basement in western Turkey consists of (typical close spaced jointing of coal and
Precambrian, Palaeozoic, and Mesozoic sedi- lignite), and breaks with a concoidal fracture.
mentary and igneous rock (Campbell 1971, Using the ASTM classification, the calorific
Brinkmann 1976) which have been subjected to value of this material would more properly
various structural and metamorphic episodes. result in it being termed a sub-bituminous B
Turkey has a great variety of structures, the coal, but it is referred to as a lignite in the
largest of which is the North Anatolian Fault local terminology.
(NAF), a major strike-slip fault system (Fig. There is an extremely sharp contact between
13.2). The NAF was formed in the late the KM2 and the overlying Sekköy Formation.
Serravallian (Sengor et al. 1985). At this time This formation is a massive, hard marlstone