冈底斯铜矿带冲江含矿斑岩的岩石化学及锆石SHRIMP年龄特征

Petrochemistry and SHRIMP U-Pb zircon age of the Chongjiang ore-bearing porphyry in the Gangdese porphyry copper belt

青藏高原南部冈底斯斑岩铜矿带冲江含矿斑岩早期为闪长岩,主期为花岗闪长斑岩及石英二长斑岩,晚期为花岗斑岩。岩石化学特征表现为早期和主期岩体主要为高钾钙碱性岩石系列,晚期岩体介于高钾钙碱和钾玄质岩石系列之间。含矿斑岩锆石SHRIMP年龄为(12.9±0.3)Ma,此年龄及前人的年龄资料表明冲江含矿斑岩体是多阶段作用形成的,第一阶段为14～15.6Ma,第二阶段为12～13.8Ma。现有冈底斯铜矿带年龄资料表明,冈底斯斑岩铜矿带成岩成矿时代在12～18Ma之间,岩浆活动时限约6Ma。

The Gangdese porphyry copper belt is a new discovered ore belt in South Tib et,China.A lot of small ore-bearing intrusions,such as Chongjiang,Qulong,Nanmu,Tinggong,Dongga and Lakange,have been found in this ore belt.The Chongjiang porp hyritic intrusion occurs in the midd le part of the Gangdese porphyry copper belt in southern Qinghai-Xizang Plateau.The Chongjiang porphyry hosts 107m illion tons of metallic copper at an average tenor ranging from 0.48%to 0.63%and about 1.27million tons of me tallic Mo,and 21tons of metallic Au.The Chongjiang porphyry could be divided into early,main and late sta ges.The early stage rock and the main stage rock are diorite and granodioritic porphyry and quartz-monzonitic porphyry,respectively,and belon g to the high-alkaline series.The main stage granodioritic porphyry and quartz-monzonitic porphyry display massive,porphyritic texture,comprising pl agioclase,K-feldspar,minor mica a nd quartz as phenocrysts.The late stage is granitic porphyry,locating between the high-alkaline series and the sh oshonitic series.SHRIMP zircon dating of quartz-monzonitic porphyry for the Chongjiang porphyry is(12.9±0.3)Ma.It represents the formation age o f the ore-bearing porphyry.Our SHRIM P zircon age is younger than the previous zircon age犤(15.60±0.52)Ma,(14.54±0.65)Ma 犦and the related Re-Os age犤(14.85±0.69)Ma,(14.04±0.16)Ma 犦.The Chongjiang ore-bearing porphyry has two different ranges of ages:12～13.8Ma and 14～15.6Ma.It is suggested that magmatic activity of the Chongjiang ore-bearing porphyry is multiperio d.The first stage is 14～15.6Ma in age,and the second stage is 12～13.8Ma.Based on our new age data,together with the previous work,it is concluded that the diagenetic and metallogenic epoch of the ore-bearing porphyries in t he Gangdese porphyry copper belt is 18Ma to 12Ma.Duration of magmatic activity of the ore-bearing porphyries is a bout 6Ma.