Chol-qeshlaghi altered area lies in the northwestern part of the post-collisional Urumieh-Dokhtar magmatic arc, NW Iran. Pervasive silicic, argillic, phyllic and propylitic altered zones appears to be intimately affil...Chol-qeshlaghi altered area lies in the northwestern part of the post-collisional Urumieh-Dokhtar magmatic arc, NW Iran. Pervasive silicic, argillic, phyllic and propylitic altered zones appears to be intimately affiliated to the fluids derivative of upper Oligocene Khankandi granodiorite. This paper is dedicated to the identification of geochemical characteristics of hydrothermal alterations, focusing on the determination of the mass gains and losses of REEs, to gain significant insights regarding the chemical exchanges prevailed between the host rocks and hydrothermal fluids. The low pH and high activity of SO4-2 ligands in silicic alteration fluids, resulting in depletion of entire REEs. Decreasing of LREEs appeared in argillic zone may attributed to reduce in adsorption ability of clay minerals in low pH;whereas HREEs enrichment in phyllic zone was inclined to put it down to the abundance of sericite(± Fe oxides). A significant reduction of Eu/Eu* ratio in silicic zone can be attributed to negligible sulfides and clay minerals as some effective agents in adsorption of released Eu+2. Factors such as changes in pH, the abundance of absorptive neomorph mineral phases, activity of ligands play an important role in controlling the distribution and concentration of REEs in Chol-qeshlaghi alteration system.展开更多
The Aghbolaq skarn deposit is located in the Urumieh-Golpayegan plutonic belt,NW Iran.The garnetite skarn(stageⅠ)has been intensely cross-cut by the magnetite-garnet skarn(stageⅡ)which were,in turn,cut and offset by...The Aghbolaq skarn deposit is located in the Urumieh-Golpayegan plutonic belt,NW Iran.The garnetite skarn(stageⅠ)has been intensely cross-cut by the magnetite-garnet skarn(stageⅡ)which were,in turn,cut and offset by the ore-hosting quartz veins/veinlets(stageⅢ).The predominance of andradite(Adr82.5–89.1)and its high Fe3+/Al ratio(up to 1685)apparently supports the high fO2,salinity and prevalence of magmatic/hydrothermal fluids involved,rather than meteoric waters,during the magnetite-garnet skarn formation.Two major groups of fluid inclusions,namely aqueous(LV,LVS)and aqueous–carbonic(LVC,LLCVC),were recognized in garnet and quartz veins that,especially in growth zones and along intra-granular trails,better display fluid inclusion assemblages(FIAs)than those in clusters.The prograde magnetite-garnet skarn was formed by the metasomatic fluid at relatively high Th(209–374℃),under a lithostatic pressure of~200 bars.The retrograde mineralized quartz veins were formed at temperatures ranging from 124℃to 256℃,by dilute and less saline(2.57–11.93 wt%NaCl eq.)hydrothermal fluids under a hydrostatic pressure of~80 bars.The fluid evolution of the Aghbolaq skarn began with an earlier simple cooling of metasomatic fluid during the prograde stage,followed by the later influx of low salinity meteoric fluids during the retrograde stage.展开更多
文摘Chol-qeshlaghi altered area lies in the northwestern part of the post-collisional Urumieh-Dokhtar magmatic arc, NW Iran. Pervasive silicic, argillic, phyllic and propylitic altered zones appears to be intimately affiliated to the fluids derivative of upper Oligocene Khankandi granodiorite. This paper is dedicated to the identification of geochemical characteristics of hydrothermal alterations, focusing on the determination of the mass gains and losses of REEs, to gain significant insights regarding the chemical exchanges prevailed between the host rocks and hydrothermal fluids. The low pH and high activity of SO4-2 ligands in silicic alteration fluids, resulting in depletion of entire REEs. Decreasing of LREEs appeared in argillic zone may attributed to reduce in adsorption ability of clay minerals in low pH;whereas HREEs enrichment in phyllic zone was inclined to put it down to the abundance of sericite(± Fe oxides). A significant reduction of Eu/Eu* ratio in silicic zone can be attributed to negligible sulfides and clay minerals as some effective agents in adsorption of released Eu+2. Factors such as changes in pH, the abundance of absorptive neomorph mineral phases, activity of ligands play an important role in controlling the distribution and concentration of REEs in Chol-qeshlaghi alteration system.
基金fully funded by the Research Bureau atthe University of Tabrizthe generous financial contribution to this work by the authorities of this bureau
文摘The Aghbolaq skarn deposit is located in the Urumieh-Golpayegan plutonic belt,NW Iran.The garnetite skarn(stageⅠ)has been intensely cross-cut by the magnetite-garnet skarn(stageⅡ)which were,in turn,cut and offset by the ore-hosting quartz veins/veinlets(stageⅢ).The predominance of andradite(Adr82.5–89.1)and its high Fe3+/Al ratio(up to 1685)apparently supports the high fO2,salinity and prevalence of magmatic/hydrothermal fluids involved,rather than meteoric waters,during the magnetite-garnet skarn formation.Two major groups of fluid inclusions,namely aqueous(LV,LVS)and aqueous–carbonic(LVC,LLCVC),were recognized in garnet and quartz veins that,especially in growth zones and along intra-granular trails,better display fluid inclusion assemblages(FIAs)than those in clusters.The prograde magnetite-garnet skarn was formed by the metasomatic fluid at relatively high Th(209–374℃),under a lithostatic pressure of~200 bars.The retrograde mineralized quartz veins were formed at temperatures ranging from 124℃to 256℃,by dilute and less saline(2.57–11.93 wt%NaCl eq.)hydrothermal fluids under a hydrostatic pressure of~80 bars.The fluid evolution of the Aghbolaq skarn began with an earlier simple cooling of metasomatic fluid during the prograde stage,followed by the later influx of low salinity meteoric fluids during the retrograde stage.
