Fluid processes in the Tesbihdere base-metal-Au deposit: Implications for epithermal mineralization in the Biga Peninsula, NW Turkey

Abstract

Abstract:Tesbihdere is one of a number of spatially close epithermal Cu-Pb-Zn-Ag-Au deposits hosted by andesites and rhyolites, typical of deposits in the Biga peninsula. Microthermometry of fluid inclusions shows a wide range of temperatures, ∼360-170 • C, and salinities, ∼10-0.5 wt.% NaCl, in the different deposits studied. Dilution of a moderately saline magmatic? fluid with meteoric water occurred at constant temperature indicating, the temperature of both fluids was controlled by the geological environment. Boiling was not a major factor, but did occur in very minor amounts. The large range of temperatures within individual samples can only reasonably be explained by variations from near lithostatic to hydrostatic pressure during vein and fracture opening. That this pressure decrease did not produce extensive boiling suggests that vein opening was gradual rather than aggressive, allowing the pressure and temperature decrease to follow a path close to the L-V boiling curve. P-T reconstruction places emplacement of these ore veins at between 300-500 m beneath the surface. Similarities of LA-ICPMS of fluid inclusions from Tesbihdere, Azitepe and Basmakci, supports the conclusion that they were part of the same contemporaneous mineralizing system. The fluids are dominated by Na, with the concentrations of K>Ca>Mg combined equivalent to the concentration of Na. The range of K/Na ratios is not consistent with the fluid inclusion temperatures as the calculated temperatures are significantly higher indicating the fluids were not close to equilibrium with the enclosing rocks.

Sulfur isotope geochemistry and mineralogy of Balcilar vein type barite-sulphide mineralization, Biga peninsula, NW Turkey

“…Boiling and negative δ 34 S values have (Table 1) been recognized here and at other deposits in the region ( [31], [32], [33], [34]). [35] suggest that fluid boiling will lead to a loss of H2 and the oxidation of the ore fluid.…”

Comment on “Origin and evolution of hydrothermal fluids in epithermal Pb-Zn-Cu + Au + Ag deposits at Koru and Tesbihdere mining districts, Canakkale, Biga Peninsula, NW Turkey” by Mustafa Cicek and Tolga Oyman, [Ore Geology Review, 2016, 78, 176–195]

“…These papers (Yilmaz et al 2010, Bozkaya et al 2014 temperature and their approach seems to be to simply take the average. This is incorrect as it leads to huge potential errors in the calculated 18 O value for the water by not knowing the correct temperature of the fluid when the quartz was precipitated.…”

The importance of supersaturated silica deposition for base-metalAu–Ag mineralisation in western Turkey

“…There appears to be only limited metal deposition at this stage. The decrease in pressure leads to adiabatic cooling of the fluid, which Bozkaya et al (2014) and Bozkaya and Banks (2015) propose for this deposit and the similar deposit at Tesbihdere. The cooling path was close to the L-V curve, hence the lack of an extensive vapour phase.…”

“…Fluid inclusion evidence shows that "gentle" boiling was occurring during the deposition of the euhedral quartz and that this was a repetitive process. There is also evidence of flashing of the fluids (instantaneous conversion of all the liquid to vapour) and this causes the precipitation of the amorphous silica bands (Bozkaya and Banks, 2015;Bozkaya et al, 2014). As silica has a negative surface charge it can readily adsorb cations from solution and the greater surface area when silica is precipitated as colloidal particles could prove effective in accumulation of ore metals.…”

“…The studies by Bozkaya et al (2014) and Bozkaya and Banks (2014) on the Tesbihdere and Arapuçandere deposits (Çanakkale) used fluid inclusion data to better understand the processes that controlled the fluid temperature and salinity and how this could be used to constrain the pressure-temperature-depth at the time of vein formation and mineralisation. The present day mining operations, at or approximately 100 m below the present surface, exploit part of the mineralisation that was originally emplaced approximately 600 m beneath the palaeosurface.…”