Whilst the presence of copper in Cyprus is well-documented, it is widely considered that there is little gold in Cyprus. This is a fallacy perpetuated from historical inaccuracies. The gold content of many of the deposits was poorly documented or not tested and so was rarely included in the historical mining statistics. There is extensive evidence that the massive pyrite deposits contain appreciable primary gold. Furthermore, the weathered zones above many deposits are highly enriched in gold and silver. For example, miners targeted “Devil’s Mud” – a narrow layer above the massive sulphide bodies – because it was highly enriched in gold and silver (presumably supergene). The Devil’s Mud Skouriotissa was investigated for precious metals in 1932 when copper and pyrite prices were depressed. Devil’s Mud was immediately identified at Skouriotissa with “areas of high- grade ore running as much as 50 ounces of gold per ton, though with very little silver, and, conversely, other areas containing 800 ounces of silver a ton and only traces of gold.” (Lavender, 1962). These discoveries led to exploration elsewhere in the Troodos Mountains and ultimately the mining of Devil’s Mud by CMC at seventeen locations, albeit most of this mining was very small scale. In 2016, the Hellenic Mining Company commissioned a gold circuit at Skouriotissa to process the oxide material in the area. This went into production in 2017.

CMC’s experience of the Devil’s Mud clearly shows that gold and silver are widespread throughout Cyprus. However, the primary pyrite ores were never exploited because the technology to extract gold and silver at that time was not advanced enough to be economically viable. This is not the case today.

Skouriotissa copper mine today

More recent work confirms that gold is widespread in the primary pyrite ore and can be quite high grade. For example: 4.98 g/t Au at Pano Lefkara (Northern Lion, 2012); and BMG Resources reported numerous gold intercepts at their Mala Prospect, including 6 m @ 3.70 g/t Au (MALRC007) and 5 m @ 2.15 g/t Au (BMG, 2014).

Chesterfield has recently announced the discovery of a gold mineralized system at its Westline target (see separate section)

Mosaic in village square, Troodos Mountains

The island of Cyprus is located in the eastern Mediterranean Sea along the southern margin of the Anatolian Tectonic Plate. The area of interest for mineral exploration is a geological feature known as the Troodos Ophiolite, a large fragment of ocean floor and associated underlying crust that has been physically obducted through serpentinite diapirism become emergent as the island of Cyprus.

Today, the Troodos Ophiolite forms an anticlinal dome. The deepest formed intrusive units (basal oceanic crust) are now the highest central hills, and the seafloor volcanic rocks and overlying sedimentary rocks are exposed around the flanks.

The deepest formed unit, called the Plutonic complex, compromises the ultramafic Harzburgite unit and an upper mafic (Gabbro) unit separated by an interlayered mafic/ultramafic unit. Overlying is the Sheeted Dyke complex compromising of steeply dipping mafic dykes, which intrude either gabbro (lower part of the unit) or basalt lava flows (upper part). The upper part of the sequences consists of two extrusive rock units, the Upper Pillow Lavas (UPL) and the Lower Pillow Lavas (UPL); the two basaltic rock units have distinct geochemical compositions.

Overlying sedimentary rocks are mostly limestone, chalk and marl dating back to the Cretaceous to Miocene.

Chesterfield is targeting both the contact between the extrusive units and the overlying sedimentary rocks and the contact between UPL and LPL for the discovery of a VHMS deposit.

Modern seafloor volcanic centres are areas of intense hydrothermal activity, which can deposit massive sulphide accumulations, commonly referred to as Volcanic-Hosted Massive Sulphide (VHMS) deposits. Ancient forms of these deposits are the exploration targets in Cyprus. The basic ore-forming processes of VHMS deposits are well understood – broadly coincident with magmatism; seawater is drawn down into the oceanic crust where it becomes progressively hotter and richer in metals and sulphur. This now enriched hydrothermal fluid then rises back towards the seafloor with the metal-sulphur either depositing along the way or erupting onto the seafloor itself as “black smokers”.

A “black smoker” venting highly mineralised hydrothermal fluid on the ocean floor.

The richest deposits are those that erupt onto the seafloor. The size and grade of a VHMS deposit are primarily controlled by the size and persistence of the hydrothermal system. The available pathways control the location of VHMS deposits for the hydrothermal fluid, i.e. faults and fractures, with particular relevance given to the main faults which control volcanic rifting.

VHMS tectonic settings (Schulz, 2012).

Deposits range in age from Early Archean (3.55 Ga) to Holocene and are also currently forming at numerous localities in modern oceanic settings.

Massive sulphide bodies typically have lensoidal or sheet-like forms, and many deposits occur in clusters close to each other.

Schematic of a typical sea floor massive sulphide lens.

Below the sulphide bodies, many but not all deposits overlie discordant sulphide-bearing vein systems (stringer or stockwork zones) that represent fluid flow conduits below the seafloor.

A zonation of metals within the massive sulphide body can also be identified from Fe+Cu at the base to Zn+Fe±Pb±Ba at the top and margins. Other features spatially associated with VHMS deposits are exhalative (chemical) sedimentary rocks, subvolcanic intrusions, and semi-conformable alteration zones.

The composition of volcanic rocks hosting individual sulphide deposits range from felsic to mafic, but bimodal mixtures are not uncommon. ‘Cyprus Type’ VMS deposits describe the mafic-ultramafic type (associated with seafloor spreading and ophiolite/ocean-floor stratigraphy and structure), with the currently producing Skouriotissa deposit being the archetypal example. Specific to “Cyprus-style” VHMS systems is a structural control along one or both margins, as well as a mantling of the deposit by a broader zone of characteristic alteration that decreases away from the deposit (Franklin et al., 1981). The alteration is dominated by chlorite, quartz, pyrite and epidote, and silicification is commonly sufficiently intense in the stockwork zone to be detected as a resistivity anomaly in geophysical data.

Cyprus VHMS deposits are composed of pyrite with varying contents of chalcopyrite and sphalerite, with rare galena (Bear, 1963). Marcasite, pyrrhotite, rutile, gold and silver are also present, with silver strongly associated with chalcopyrite. Many of the deposits have been weathered with copper oxides, chalcocite, covellite, bornite, digenite, vallerite, tenorite, as well as jarosite, magnetite and hematite as the main secondary minerals (Pantazis, 1979).

VHMS deposits and occurrences in Cyprus are likely associated with gossans and other useful exploration vectors such as gossans, exhalites, limonite and ochre.