【摘要】 滇西金沙江-哀牢山成矿带发育众多与富碱侵入岩密切相关的斑岩矿床。六合正长斑岩产于该成矿带中段,为贫矿富碱斑岩。在岩相学基础上,对六合正长斑岩中的黑云母、角闪石、锆石进行了矿物学研究,厘定了矿物结晶的温压条件、岩浆氧逸度和含水量等关键要素,并结合全岩地球化学和前人研究成果,讨论了制约滇西富碱斑岩成矿的条件。六合正长斑岩中的黑云母富镁（MgO=12.98%¹4.83%）、铝（Al₂O₃=14.18%¹6.52%）,Fe²⁺/(Fe²⁺+Mg)=0.29⁰.31,矿物温压计测得黑云母的结晶温度为615⁶69℃,形成压力为103¹65 MPa,形成深度为3⁵ km（平均深度为4.2 km）。角闪石富铁（FeO=21.75%²2.21%）、钙（CaO=10.14%¹0.49%）,属浅闪石质-韭闪石质角闪石,形成温度为817⁸43℃,形成压力为158¹91 MPa,形成深度为5⁶ km（平均深度为5.9km）。通过角闪石成分限定岩浆氧逸度（ΔFMQ）为+1.12⁺1.27。岩体中的岩浆锆石结晶温度为687¹ 098℃,Ce⁴⁺/Ce³⁺=11.18⁵4.78（平均值<50）,δEu=0.14⁰.81。正长斑岩中角闪石以斑晶产出,全岩Dy/Yb值与SiO₂含量呈负相关性,La/Yb值与SiO₂含量呈正相关性,且δEu=0.97¹.00,说明六合岩浆在早期结晶大量角闪石,鲜有斜长石分离结晶。以上分析显示六合正长斑岩具有低氧逸度、高含水量的特征。对比斑岩矿床中含矿岩石的矿物学特征,认为六合正长斑岩不具有形成斑岩型矿床的潜力。更多还原

【Abstract】 A lot of porphyry deposits, related to potassic intrusions closely, occur in the Jinsha-Ailaoshan metallogenic belt, western Yunnan. Liuhe orthophyre is barren magmatic rock and is located at the center of the belt.Based on petrography, the authors studied mineral characteristics of biotite, amphibole and zircon in Liuhe orthophyre, and investigated mineral temperature-pressure condition, magmatic oxidation state and water content. Depending on geochemical data and previous studies, the authors discussed the constraining condition for mineralization of potassic intrusions. Biotite has high MgO（ 12. 98% 14. 83%）, CaO（ 14. 18% 16. 52%） content, with Fe²⁺/( Mg + Fe²⁺) ratios being 0. 29 0. 31. Mineral thermobarometric calculations show that crystallization temperatures of biotite are 615 669℃ under the pressure of 103 165 MPa and at the depth of 3 5 km（ 4. 2 km on average）. Amphibole consists dominantly of endenite and pargasite. Crystallization temperatures of amphibole are817 843℃ under the pressure of 158 191 MPa and at the depth of 5 6 km（ 5. 9 km on average）.Oxygen fugacities（ ΔFMQ） of magmas, constrained by chemical composition of amphibole, are + 1. 12 + 1. 27. Crystallization temperatures of magmatic zircons are 687 1 098℃ and Ce⁴⁺/Ce³⁺ ratios are 11. 18 54. 78( Ce⁴⁺/Ce³⁺<50 on average), δEu = 0. 14 0. 81（ δEu < 1）. Liuhe orthophyre has δEu ratios of 0. 97 1. 00, and whole-rock Dy/Yb ratios have negative relation and La/Yb ratios have positive relation with SiO₂ values, respectively. In addition, amphibole occurs as phenocrysts. These features indicate that a lot of amphibole crystallized at the early stage whereas crystallization of plagioclase was suppressed. The authors hold that Liuhe orthophyre had low oxygen fugacity and high H₂O content. Compared with mineral characteristics of fertile magmas of porphyry deposits, Liuhe orthophyre has no potential to form porphyry deposits.更多还原