Processes that Concentrate Mineral Resources

集中矿产资源的过程

A number of processes occur in igneous rocks to provide accumulations of otherwise rare elements or minerals. Most minerals are made up of the eight abundant elements, and most surface minerals are silicates. Our capacity to find the "needle in the haystack" of the metals such as gold, silver, etc. comes from the fact that there are igneous processes which tend to concentrate them in one location.

火成岩中发生多种过程，以形成其他稀有元素或矿物的积累。大多数矿物由八种常见元素组成，大多数地表矿物是硅酸盐。我们能够找到金、银等金属的“针在 haystack 中”的能力，源于火成过程倾向于将它们集中于一个地点。

The concentration of some of the metals comes from the fact that their ions are heavier and tend to sink to the bottom of the molten magma. Later in the process of magma cooling, water and some of the more volatile elements that are not included in the earlier crystallation processes become more concentrated in the remaining melt. In these enriched fluids, ion migration can contribute to the formation of large crystals, sometimes centimeters to meters in size. The resulting rocks that are formed from these large crystals are called pegmatites. Some minerals, like amblygonite, are found only in such pegmatites because they concentrate what would otherwise be trace constituents.

一些金属的浓度来源于它们的离子较重，倾向于沉降到熔融岩浆的底部。在岩浆冷却过程中，水和一些未包含在早期结晶过程中的挥发性元素变得更加集中在剩余的熔体中。在这些富集的流体中，离子迁移有助于形成较大的晶体，有时可达厘米到米的大小。由这些大晶体形成的岩石称为 pegmatites。一些矿物，如 amblygonite，仅存在于这样的 pegmatites 中，因为它们会浓缩其他本应是痕量成分的物质。

Concentration frequently occurs from hydrothermal solutions. The hydrothermal deposits are thought to arise when hot, metal-rich fluids in the late stages of magma solidification can migrate large distances through the surrounding rock. As the fluid moves along fractures or bedding planes, the metal ions can precipitate from the solution. Many of the productive deposits of gold, silver and mercury are formed as hydrothermal vein deposits.

凝固时常由热液溶液形成。热液矿床被认为是在岩浆凝固的晚期阶段，富含金属的流体能够迁移很长的距离通过周围的岩石。当流体沿着裂隙或层理面流动时，金属离子可以从溶液中沉淀出来。许多金、银和汞的富产矿床都是形成于热液脉矿床。

Pegmatites

Pegmatites（矿物名）

Since the vast majority of the materials composing the Earth's surface are composed of the big 8 elements and the silicates that are made from them, the finding of most of the other elements and minerals occurs mainly because there are processes that concentrate these rarer substances in particular places. When you see examples of large gems and crystals, a word that keeps appearing is "pegmatite", because most large crystals of otherwise rare materials usually occur in pegmatites.

由于构成地球表面的大多数材料主要由八大元素和由它们形成的硅酸盐组成，因此大多数其他元素和矿物的发现主要是因为存在将这些稀有物质集中到特定地区的过程。当你看到大宝石和晶体的例子时，一个反复出现的词是“pegmatite”，因为大多数稀有材料的大型晶体通常出现在pegmatites中。

The word "pegmatite" is not mineral-specific, but refers to igneous rocks that form in the final stages of the crystallization of molten magma. You could visualize a pocket in a large pool of magma that might be the last to crystallize because of a lower melting temperature, and which has a different concentration because the materials have a different density or some other property that separated them. That pocket might have the luxury of a long time period free of disturbances so that it slowly crystallized into large crystals. That description would be enough to bring Minas Gerais, Brazil into the minds of many geologists and gemologists, since the remarkable pegmatites of that region have been the source of most of the world's large crystals of beryl, chrysoberyl , topaz , tourmaline and spodumene .

‘ pegmatite ’这个词并不特指某种矿物，而是指在熔融岩浆结晶的最后阶段形成的火成岩。你可以想象在一个巨大的岩浆池中有一个口袋，可能是由于较低的熔点而成为最后结晶的部分，由于材料密度不同或其他性质的差异，它们被分离出来。这个口袋可能有足够长的时间处于未受干扰的状态，从而缓慢结晶形成大晶体。这种描述足以让许多地质学家和宝石学家联想到巴西的米纳斯吉拉斯州，因为该地区非凡的 pegmatite 一直是世界上大多数大晶体的来源，这些晶体包括碧玺、金绿石、托帕石、电气石和锂辉石。

A pegmatite can generally be recognized by the large crystals present, and in fact the working definition of a pegmatite is a rock in which most of the material is made up of crystals at least a centimeter in diameter. Contributing to the formation of large crystals, other than a slow crystallization process, is the fact that in the melt the crystallization of early materials leaves pockets of hot water which collect mobile ions into concentrated solutions. The higher mobility of the ions in the water, compared to inclusion in the molten rock of the magma, allows them to form large crystals more rapidly.

pegmatite 通常可以因其大晶体而被识别，事实上，pegmatite 的定义是指主要由至少直径为一厘米的晶体组成的岩石。除了缓慢结晶过程外，形成大晶体的另一个因素是，在熔体中，早期物质的结晶会留下热水的空腔，这些热水能够将移动的离子浓缩成溶液。相比于被包含在熔岩中的离子，水中的离子具有更高的移动性，从而能够更快地形成大晶体。

参考：Geology.com，伟晶岩