Summary:
The Apliki copper deposit in Cyprus is part of the Skouriotissa mining
district, which constitutes the sole exploitation and processing site for
copper production on the island. Mining activity at Apliki, from 1960 to 1974,
has resulted to the production of 1,650,000 tons of copper ore. An acidic pit
lake was created as a result of open pit mining and the subsequent supergene
alteration of sulphide ore.
The focus of the present dissertation is the study of the geology of the Apliki
deposit and the environmental impact of its past exploitation. It also aims to
contribute to the synthesis of a geo-environmental model for Cyprus–type
massive sulphide deposits.
In order to achieve these objectives a sampling from the mineralization zone,
efflorescence salts and waters from acidic open pit lake were undertaken
followed by laboratory testing using techniques of AAS, ICP–MS, ICP-AES, XRD,
SEM, RAMAN, EPMA and sulfur isotope analysis.
The mineralization is hosted within the sequence of lower pillow lavas of the
Troodos ophiolite complex. The mineralization zone is bounded by two N-S
striking sub–parallel faults. The pillow lavas at Apliki possess the same
argillic alteration as the sequence of lower pillow lavas of the Troodos
ophiolite.
The following sectors are identified in the mineralization zone:
(a) A stockwork zone
(b) Veins of amorphous silica
(c) Late–stage veins of gypsum
The stockwork ore is hosted within brecciated chloritized lavas. Weak
silicification is observed in the upper parts of the brecciated lavas. Pyrite,
marcasite, chalcopyrite, sphalerite and pyrrhotite are the main mineral
constituents with quartz as the main gangue. Copper grades range between 0,01
to 3,5% and S between 0,1 to 16%. Open–space filling jasper is observed all
along the mineralization zone.
The main mineralogical components of the amorphous silica zone are kaolinite,
Na-, Na–Mg- and Mg-sulphates. The amorphous silica of the Apliki deposit may be
correlated with silica deposits found in the submarine hydrothermal vent
systems of Galapagos Rift and Southwest Pacific Ocean.
Sheeted veins of gypsum, develop on a N–S direction and occur in the western
part of the mineralized zone, with a thickness ranging between a few
centimeters to half a meter. The δ34S values of gypsum sulphur (5,40‰ to 6,90‰)
are within the δ34S range (δ34S between -1,1‰ to +8,20‰) of sulphides of
Cyprus-type ore deposits range indicating that sulphur is derived from a late
stage hydrothermal fluid and not from Cretaceous water.
Weathering of the sulphide ore has generated extensive efflorescence salts all
along the mineralization zone, mainly as a mixture of various mineralogical
phases, and intense acid mine drainage. Iron, copper, magnesium and aluminum
sulphates were identified by combined XRD, SEM and RAMAN techniques. The
predominant minerals amongst the sulphates are melanterite, copiapite,
chalcanthite, langite, epsomite and alunogen. Calcium, sodium and magnesium
sulphates (e.g. gypsum, thenardite, bloedite, epsomite) are the main mineral
constituents of efflorescence occurring at the lower levels of the open pit.
The chemistry of the open pit lake waters demonstrates low pH values (pH 2,6
-3,3) with high concentration of sulphates (16330 to 18850 mg/L) and metals,
which exceed substantially the regulatory limits for irrigation and potable
water.
Laboratory treatment tests were carried out using ground limestone as a
neutralizing agent. The ground limestone is used for building construction at
the Mitsero and Latouros quarries. The water pH increased from 3 to 9, while
the concentration of heavy metals decreased to acceptable limits for irrigation
water, with the notable exception of Mn and sulphates.
Keywords:
Volcanic–hosted Cyprus type massive sulphide ore, Troodos Ophiolite, Supergene sulphide alteration; Efflorescence; Acid mine drainage, Sulphur-isotopic composition of gypsum; Amorphous silica, Neutralization tests of acidic open–pit lake waters
