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Fig. 2. Pillow lava sequence intruded by dikes
pillow lavas and a few dykes (Fig. 2). Most pillow lavas contain
olivine phenocrysts that are commonly altered to calcite and zeolite-
facies minerals. The boundary between the sheeted dyke complex
and the lower pillow lavas is formed by a transition zone often
referred to as the basal group.
Cyprus was one of the worlds largest producers of asbestos
associated with the harzburgites of the Troodos ultramafic
sequence. Asbestos occurs in veins within brecciated zones of
serpentinized harzburgite, mainly as the hydrated magnesium
silicate mineral chrysotile. Near the contact of the harzburgites and
dunites, small chromite bodies occur either as isolated pods and
layers in the dunite or in the harzburgite within dunite lenses.
Typically these ores contain 4796 Cr,O, and a Cr/Fe ratio of 2.7
(Greenbaum 1977) after concentration. Massive metallic sulphide
deposits are nearly all confined to the contact of the lower and
upper pillow lavas (Constantinou and Govett 1973). Pyrites and
marcasites are the primary sulphides with minor amounts of
chalcopyrites associated with traces of gold and silver. The main
secondary minerals formed due to secondary enrichment and
leaching are chalcocite, covellite and bornite. These sulphide
deposits are thought to have formed near a submarine rift by
volcanic exhalative processes which find their modern analogy in
the 'black smokers' found near the mid-atlantic ridge. Ochre locally
overlies the sulphide ore deposits and are regarded as a sub-aqueous
oxidation product of these sulphides. Umbre, defined as a
manganese iron rich sediment, is found on top of the upper pillow
lavas (Constantinou and Govett 1972).
SPECTRAL STRATIGRAPHY
The aim of this section is to establish spectral characteristics that
can be used to differentiate the main lithological units that
encompass the ore bodies of interest. First we measured and
described rock spectra of the different units after which we
measured soil spectra. These were measured with the Portable
Infrared Mineral Analyzer (PIMA II); a dual field-of- view handheld
field spectroradiometer that covers the 1.3 to 2.5um wavelength
region with a 7-10nm spectral resolution and a 2.5nm sampling
interval. In thsi paper these spectra will not be discussed at length.
The reflectance spectroscopy, however, shows that it is theoretically
possible to discriminate the different lithological units based on the
soils that develop on them. It should be noted that the outcrops are
Wavelength (Microns)
Thickness km Ümbers 13 1.5 13 1.9 2.1 23 2.5
Upper Pillow lavas
Lower Pillow lavas
Gabbro
5-1
Layered gabbro
Fig. 3. Stacked spectral sequence through the ophiolites
mostly sparse as is the vegetation cover, thus the major contribution
to the image characteristics is thought to come from the soils.
Another important aspect is the intermixed nature of the rock types
within the units. The different units, however, can be considered
mixtures of several rock types. For example the basal group is
composed of diabase dykes and andesitic pillow lavas but also
dykes occur in the lower pillow lava sequence. A spectral section
through the Troodos ophiolite sequence was measured in the field
and is shown in Fig. 3 in the form of stacked spectra. In this figure,
the dark grey levels indicate low reflectivity whereas the bright
areas are high reflectivity. Each line represents one of a total of 54
PIMA spectra through the ophiolite sequence.
200
Upper pillow lavas
mem Gabbro
———7 Harzburgite
Dunite
tw Lower pillow lavas
————————— Basal Group
Shade
Reflectance (D.N.)
04 0.8 1.2 1.8 2 24
Wavelength (Microns)
Fig. 4. TM spectra of major geologic units
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
