Geochemical Behaviour of Rare Earth Elements in the Erdaogou Gold Deposit

The study of rare earth element pattern in rhyolites of the Erdaogou gold deposit located in western Liaoning Province indicates that the REE pattern in unaltered rhyolite is characterized by typical enrichment in LRE and minor negative Eu anomaly, but altered rhyolites are characterized by distinct Eu negative anomaly, except Eu, and the other REE is similar to that in unaltered rhyolite. The reason of formation of sharp negative Eu anomaly in altered rhyolite is that secondary minerals are able to accommodate RE(3+) and not to accommodate Eu2+ during alteration process. The REE pattern in fluid formed by mixing of magmatic water with meteoric water is characterized by low REE contents, enrichment in LRE and sharp negative Eu anomaly.

Geological,Fluid Inclusion,H-O-S-Pb Isotope Constraints on the Genesis of the Erdaogou Gold Deposit,Liaoning Province

The Erdaogou gold deposit is located in the conjuncture of North China Carton and Xingmeng orogenic belt.The ore-forming process of Erdaogou gold deposit is divided into three stages(ⅠtoⅢ),which are quartz-pyrite stage(stage I),quartz-polymetallic sulfide stage(stage II)and quartz-calcite stage(stage III).Two types of fluid inclusions is distinguished in the ore-forming stage,i.e.,aqueous type(W-type)and aqueous-carbonic type(C-type)inclusions.From the stageⅠtoⅢ,the homogenization temperature of fluid inclusions are respectively 334-395,214-364 and 172-272℃,with salinities of 7.72 wt.%-11.23 wt.%NaCl equiv.,0.20 wt.%-23.18 wt.%NaCl equiv.,and 0.35 wt.%to 5.25 wt.%NaCl equiv.The ore-forming fluids of the Erdaogou deposit have the characteristics of medium-low temperatures,moderate salinities and low densities.And the fluids belong to the CO,-H2O-NaCl system.The values ofδ34SV-CDT in sulphide samples at different stages(stages I to III)are between-2.2‰ to 2.3‰,indicating sulfur source from magma volatiles or subvolcanic rock leaching.The lead isotopes suggest that ore-forming metals may be derived from a mixture of lower crust and mantle materials.Oxygen and hydrogen isotope data at Erdaogou indicate that magmatic fluid and meteoric water may both be involved in the hydrothermal system.Based on the geological characteris-tics,fluid inclusion results,stable and radiogenic isotope results of Erdaogou gold deposit,we believe that the temperature decrease,fluid boiling are the key factors leading to the ore precipitation and the genetic type of Erdaogou gold deposit is low-sulfidation epithermal deposit.