岩浆热场与热液多金属成矿作用

岩浆热场指的是很短时间内一个局部地区出现的岩浆活动使该区域地热梯度明显上升,形成局部区域的瞬间热场。热场的规模通常很小,离岩体约几米至几千米。范围、规模和形状与侵入体的温度、成分、形态、大小、侵入深度以及流体、构造、围岩性质等有关。岩浆热场最重要的意义在于它是流体赖以上升的场所。岩浆热场不同于地热场的一个重要区别是,岩浆热场往往伴有流体的活动,是流体循环、上升、汲取地壳中有用金属元素的场所。文中讨论了岩浆热场与热液多金属成矿之间的关系,讨论了岩浆热场在岩浆热液矿床、热泉型矿床、热水沉积矿床以及变质热液矿床成矿过程中的作用。岩浆热场对于热液多金属成矿作用的影响是非常明显的,它从一个新的角度解释了成矿为什么是多金属、多成因、多来源等问题。文中强调指出,岩浆热场说解释了为什么大规模岩浆活动与大规模成矿作用密切相关,指出大规模岩浆活动产生的热效应不是1+1=2,而是1+12的效果。即它可以在一个局部范围内把岩浆热场从一个开放体系变为封闭体系,在这个封闭体系内,固岩可以达到更高的温度,热可以持续更长的时间,促进热场范围内流体的对流循环,使流体可以从围岩中汲取尽可能多的有用金属元素,起到单个岩浆无法比拟的效果。许多大型一超大型的多金属矿床即可能与这种作用有关。从热场说角度来看,大规模岩浆活动的成矿潜力几乎是无可限量的。文中还讨论了岩浆热场说的原理及应用中存在的问题,指出岩浆热场说与成矿的关系非常值得关注,它也许可以改变目前对成矿作用的某些固有认识,开拓出一个新领域。

Magma-thermal field and hydrothermal polymetallic mineralization

The magma thermal field is an instantaneous thermal field in a very short period of time and in a local region caused by magma, which makes geothermal gradient obviously high. The scale of the magma thermal field is small, usually a few meters to several kilometers away from intrusions. The scope, scale and shape of the magma thermal field is related to temperature, composition, shape, size, depth of the intrusion, and fluid, structure, properties of surrounding rock and so on. The magma thermal field is a place where fluids rise. It is an important difference which makes the magma thermal field is different from the geothermal field that the magma thermal field often accompanied by fluid activity, is a place of fluids circulation, rise and absorbing useful metal elements in the crust. This paper discussed the relationship between the magma thermal field and polymetallic hydrothermal mineralization, and the role of magma thermal field in the magmatic hydrothermal deposit, hydrothermal sedimentary deposit, hot spring deposit and metamorphic hydrothermal deposit. It explains the mineralization from a new perspective. It may explain many difficult and controversial issues, such as the problem of multiple sources, metals and causes, why gold-copper deposits and tungsten-tin deposits can be associated, why some granites related to mineralization but others are not, why mineralization lag behind of granite, the genesis of Calin-type gold deposit, the problem of some stratabound SEDEX type and MVT type Pb-Zn deposit reenrichment, why some skarn is away from the intrusion, and so on. This paper indicates the reasons why large-scale magmatic activity and large-scale mineralization is closely related. It makes magma thermal field from an open system into a closed system in a local scope. In this closed system, the temperature of the surrounding rock can achieve higher, heat can last longer. It promotes the fluid convection circulation in the range of this magma thermal field, makes the fluid can draw useful metal element as much as possible from the surrounding rock with incomparable effect. Many large super-large polymetallic deposits may be associated with this kind of mineralization. From the angle of the magma thermal field, metallogenic potentiality of large-scale magmatic activity is virtually unlimited. This paper also discussed existing problems about principles and applications of the magmatic thermal field, and pointed out that the relationship between the magma thermal field and mineralization is notable. It may be able to change our current deep-rooted understanding of metallogeny, carved out a new field, advanced deposit studies into a new stage.