The White Pine Copper Deposit, Ontonagon County, Michigan.
The White Pine Copper Deposit, Ontonagon County, Michigan.
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密歇根州昂托纳贡县的白松铜矿床。
作者：
W. S. White;J. C. Wright
铜主要存在于矿物辉铜矿中，位于密歇根州昂托纳贡县白松附近的诺努什页岩最下面的岩层中，面积达数平方英里。诺索什页岩形成于基韦纳湾晚期，厚约600英尺，主要由灰色粉砂岩组成。它覆盖着2300至5500英尺的红色砂岩和砾岩，即铜港集团。这一建造反过来又覆盖在中基韦纳湾波蒂奇湖熔岩系列之上，其中产有苏必利尔湖南岸著名的自然铜矿。白松铜矿位于主要天然铜矿西南偏西方向45至70英里处。白松铜矿的含铜层主要位于下部20至25英尺的努内什页岩中。这一含铜带在当地被划分为四个地层单位，按升序为下部砂岩(铜港砾岩最上层)、分离页岩、上部砂岩和上部页岩。上部页岩和部分页岩中的层序几乎相同，表明存在旋回沉积作用。这一层序和沉积相的分布可归因于两次淹没，相隔一次浮现的三角洲地区。实际上，所有的铜都赋存于上、分页岩中，除了靠近白松断层的一小块区域，那里的上、下砂岩中都有丰富的铜。它存在于五个不同的层面，数量平均在1%到3%之间。每一层中铜的总量一般在厚度较大的地方较高，而厚度似乎在远离古三角洲主河道的凹陷区域最大。页岩层的铜含量通常会随着其含砂量的增加而下降。个别含铜层厚1到3英尺的范围可以用平方英里来测量。铜在上下砂岩层中的局部赋存状态可以合理地解释为从白松断层沿相对渗透性砂岩的倾角向上倾斜到邻近背斜顶部的热液输送的结果。另一方面，铜在离层和上部页岩中的分布似乎完全与当地的构造、断层和岩石渗透率无关。对于整个地区来说，控制因素是岩性和地层学。铜可能是掉进或沉淀在原始泥浆中的；可以想象，它可能已经用精致的细节取代了如此沉积的其他东西。
Copper, largely in the mineral chalcocite, is found in the lowermost beds of the Nonesuch shale over many square miles near White Pine, Ontonagon County, Mich. The Nonesuch shale, of late Keweenawan age, is about 600 feet thick and is composed largely of gray siltstone. It overlies 2,300 to 5,500 feet of red sandstones and conglomerates, the Copper Harbor conglomerate. This formation, in turn, overlies the middle Keweenawan Portage Lake lava series, in which occur the famous native-copper deposits of the south shore of Lake Superior. The White Pine mine is 45 to 70 miles west-southwest of the principal native copper mines.The copper-bearing beds at White Pine are primarily in the lower 20to 25 feet of the Nonesuch shale. This cupriferous zone is divided in local usage into four stratigraphic units, which are, in ascending order, the lower sandstone (the uppermost bed of the Copper Harbor conglomerate), the parting shale, the upper sandstone, and the upper shale. The sequence of beds is almost identical in the upper and parting shales, suggesting cyclic sedimentation. This sequence and the distribution of sedimentary facies are attributed to two submergences, separated by an emergence, of a deltaic area.Practically all the copper occurs in the upper and parting shales, except in a small area near the White Pine fault where it is abundant in the upper and lower sandstones. It is present in five different layers in amounts that average from 1 to 3 percent. The total amount of copper in each bed is generally higher where the bed is thick, and thickness, in turn, seems to be greatest in areas that were hollows away from the main channel or channels of the ancient delta. Copper content of the shale beds typically decreases as their sand content increases. The extent of individual copper-bearing beds 1 to 3 feet thick is measurable in square miles.The local occurrence of copper in the upper and lower sandstone beds can be reasonably explained as the result of hydrothermal transportation from the White Pine fault up the dip of the relatively permeable sandstone to the crest of an adjacent anticline. Distribution of copper in the parting and upper shales, on the other hand, seems to be completely independent of local structure, faults, and rock permeability. For the area as a whole the control is lithologic and stratigraphic. Probably the copper was dropped into or precipitated within the original mud; it may conceivably have replaced with exquisite detail something else that was so deposited.