Geology Reference
In-Depth Information
18 Carbonate Rock Resources, Facies, Weathering, Preservation
the calcite/dolomite/non-carbonate triangle. Subdivid-
ing carbonate rocks according to their chemical com-
position (e.g. CaO, MgO, SiO
2
, and P
2
O
5
) is essential
for the economic use of limestones and dolostones.
Textural classifications (Chap. 8) are of value in
characterizing petrophysical rock properties related to
fabric and grain/matrix ratios (e.g. weathering resis-
tance of building stones). The incorporation of addi-
tional criteria (rock color, grain size, sorting, porosity)
in the Dunham classification is recommended for dis-
tinguishing carbonate rocks of different physical and
chemical qualities. Dearman (1981) proposed an engi-
neering classification of carbonate rocks based on a
combination of textural and compositional criteria with
material and mass properties. Understanding geo-
technical properties (e.g. compressive strength) requires
classifications that combine petrography, textural and
diagenetic features and technological data (Rashed and
Sediek 1997; Bell et al. 1999).
The industrial use of carbonate rocks depends on physi-
cal and chemical properties. These properties are the
result of the sedimentary and diagenetic history of the
rocks. In many cases, the 'primary (depositional) fa-
cies' influencing the course of diagenesis are impor-
tant controls for specific physical-chemical rock crite-
ria. Microfacies analysis assists in understanding these
controls. The study of causal relationships between
microfacies data and specific rock properties will be
an important tool of future work. This chapter demon-
strates some examples illuminating the potential of
applied facies analysis in this field.
18.1 Industrial Use of Carbonate
Rocks
The industrial use of carbonate rocks is maxifold, in-
cluding chemical and metallurgical industries, construc-
tion and concrete materials as well as agricultural uses
(Boynton 1980; Leidner 1994). Limestones and dolo-
mites have the third rank in the amount and value of
globally extracted mineral resources.
18.2 Exploration and Exploitation of
Carbonate Rocks
Classifications.
The specific uses of carbonate rocks
need specific classifications related to the chemical and
mineralogical composition and petrophysical proper-
ties (porosity, pore size and pore throat distribution,
permeability; see Sect. 7.5.3). Industrial use requires
categories describing compositional intergradations
caused by differences in the relative amounts of calcite
and dolomite and by various amounts of non-carbon-
ate minerals (e.g. Bissell and Chilingar 1967; Correns
1968; Bentz and Martini 1968; Flügel and Haditsch
1975; Langbein et al. 1982; Lobitzer and Surenian
1984). These categories are determined by national and
international norms (e.g. Gotthart and Kasig 1996;
Oates 1998). Differences in chemical composition can
be expressed on the basis of Ca/Mg weight ratios or
using percentages of calcite, dolomite and clay. Dif-
ferent limits are used in order to define subgroups within
Economic exploitation of carbonate rocks for indus-
trial use should consider
•
relations between depositional facies, diagenetic
history and rock properties,
•
differentiation of facies types related to differences
in physical and chemical criteria, and
•
transformation of these facies types into limestone
and dolomite categories that are of interest to com-
panies and clients.
Practical steps involved are:
•
Field work.
Facies mapping and sampling of out-
crops exhibiting lithofacies and microfacies varia-
tions of the carbonates.
•
Geochemical prospecting.
Chemical data from out-
crops and wells are important in the evaluation of
the industrial use of carbonate rocks. Common com-
