1�� School of Earth Science and ��esources��Chang'an University��Xi'an 710054��China; 2�� Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits��ML�ң�Xi’an 710054��China

This paper mainly researches the geochemical characteristics of isotope and ��EE of hydrothermal dolomite and barite from dolomite- sulfide ore and barite- sulfide ore of Mayuan Pb- - Zn deposit�� The result shows that the δ 13 C PDB ��δ 18 O SMOW and 87 Sr/ 86 Sr values of dolomites are ��2. 51 ×10 ^��3 ��0. 93 ×10 ^��3 �� 17. 55 ×10 ^��3 ��23. 24 × 10 ^��3 and 0. 711 46�� respectively�� indicating the C�� O may derive from the dissolution of Sinian carbonates�� and the Sr derived from crust��such as the basement and the Paleozoic clastic rocks rich in radioactive strontium�� The ��EE patterns of the dolomites are with obvious positive anomaly of Eu (δEu average of 1. 415)��indicating the dolomite- sulfide ore- forming fluid characterised by basinal hydrothermal fluid�� The δ 34 S values (average of 33 × 10 ��3 ) of barite are enriched in 34 S and narrowly distributed��implying that the sulfur may have been derived from marine sulfate�� The 87 Sr/ 86 Sr ratios (0. 709 18 and 0. 709 71) of barite also indicate that the Sr is mainly derived from seawa- ter with little from crust�� The ��EE patterns of the barites are with obvious negative anomaly of Ce (average δCe of 0. 255) and weak positive anomaly of Eu (δEu average of 1. 43)��suggesting that the barite- sulfide ore- forming flu- id might be seawater (or meteoric water) mixed with basinal hydrothermal fluid�� The precipitation of the dolomite- sulfide ore and the barite- sulfide ore might be related to the fluid mixing of basin hydrothermal fluid and seawater (or meteoric water) at different ratios��