Fluid Inclusion Characteristics of the Kışladağ Porphyry Au Deposit, Western Turkey

Abstract

The deposit occurs in a mid-Miocene monzonite magmatic complex represented by three different intrusions, namely Intrusion 1 (INT#1), Intrusion 2 (INT#2, INT #2A), and Intrusion 3 (INT#3). Gold mineralization is hosted in all intrusions, but INT#1 is the best mineralized body followed by INT#2. SEM-CL imaging has identified two different veins (V1 and V2) and four distinct generations of quartz formation in the different intrusions. These are: (i) CL-light gray, mosaic-equigranular quartz (Q1), (ii) CL-gray or CL-bright quartz (Q2) that dissolved and was overgrown on Q1, (iii) CL-dark and CL-gray growth zoned quartz (Q3), and (iv) CL-dark or CL-gray micro-fracture quartz fillings (Q4). Fluid inclusion studies show that the gold-hosted early phase Q1 quartz of V1 and V2 veins in INT#1 and INT#2 was precipitated at high temperatures (between 424 and 594 °C). The coexisting and similar ranges of Th values of vapor-rich (low salinity, from 1% to 7% NaCl equiv.) and halite-bearing (high salinity: >30% NaCl) fluid inclusions in Q1 indicates that the magmatic fluid had separated into vapor and high salinity liquid along the appropriate isotherm. Fluid inclusions in Q2 quartz in INT#1 and INT#2 were trapped at lower temperatures between 303 and 380 °C and had lower salinities between 3% and 20% NaCl equiv. The zoned Q3 quartz accompanied by pyrite in V2 veins of both INT#2 and INT#3 precipitated at temperatures between 310 and 373 °C with a salinity range from 5.4% to 10% NaCl eq. The latest generation of fracture filling Q4 quartz, cuts the earlier generations with fluid inclusion Th temperature range from 257 to 333 °C and salinity range from 3% to 12.5% NaCl equiv. The low salinity and low formation temperature of Q4 may be due to the mixing of meteoric water with the hydrothermal system, or late-stage epithermal overprinting. The separation of the magmatic fluid into vapor and aqueous saline pairs in the Q1 quartz of the V1 vein of the INT#1 and INT#2 and CO2-poor fluids indicates the shallow formation of the Kışladağ porphyry gold deposit.

Tourmaline Composition of the Kışladağ Porphyry Au Deposit, Western Turkey: Implication of Epithermal Overprint

“…In conclusion, the chemical data of tourmalines from the Kışladag gold deposit has helped in understanding its formation during various alteration/mineralizing (potassic/propylitic), phyllic and argillic stages in a telescoped porphyry/epithermal system. The data is consistent with the fluid inclusion data for Kışladag deposit [13] that supported the process of an epithermal overprint of the porphyry mineralization.…”

“…The Biely Vrch tourmaline crystallized from an unusual Cl-rich high-temperature fluid [38], whereas tourmaline from the sandstone cement in Poland was related to the low-temperature diagenesis of evaporite sediments inducing reactions of quartz and clay minerals [39]. The fluid inclusion study at the Kısladag deposit [13] revealed a high-temperature, highly saline fluid was responsible for the formation of most of the gold-bearing veins. It can be ruled out that this fluid was released from fluid inclusions during the late epithermal overprint and incorporated into the Cl-rich tourmaline.…”

“…The main geological and mineralization characteristics and fluid inclusion data of the deposit were given in previous studies [12,13,16,17]. The geological features of the Kışladağ deposit have been studied in detail by [12] and classified as an Au-only porphyry deposit due to the absence of significant amounts of Cu-mineralization.…”

“…Tourmaline exists throughout the deposit and in all phases associated with the three intrusions except for late vuggy silica which is associated with the advanced argillic alteration in volcanoclastic rocks [16], which is most common in volcanic rocks adjacent to INT#1 forming an outer alteration shell ( Figure 2). The stockworks containing Au are commonly associated with tourmaline-quartz veins, banded quartz-pyrite-tourmaline veins that are cut by sooty pyrite ± marcasite-tourmaline veins [12,13,16].…”

“…The deposit consists of porphyry-style Au mineralization connected with a series of overlapping sub-volcanic monzonite intrusions (intrusive #1 to intrusive #3, [12]). In a recent study [13] related to fluid inclusions, it was proposed that the different quartz veins associations and the temperatures and salinities supported the process of an epithermal overprint of the primary porphyry mineralization. Figure 1.…”