A mechanism for framboid formation as illustrated by a volcanic exhalative sediment |
| |
| Authors: | G R Taylor |
| |
| Institution: | (1) School of Applied Geology, University of New South Wales, Kensington, Australia |
| |
| Abstract: | A sequence of oxidate facies sediments associated with a cupriferous massive sulphide deposit in the Solomon Islands is the product of precipitation at an exhalative fluid/seawater interface. A siliceous sinter bed within the sediments contains magnesioferrite spheroids having a distinctive framboid texture. Scanning electron micrographs of the spheroids show an internal structure of parallel rods composed of sub-spherical microcrysts. The formation of the magnesioferrite framboid texture is ascribed to the coagulation of magnetic iron hydroxide gel particles due to magnetic attraction but facilitated by the presence of a strong electrolyte. By analogy a simple mechanism to account for pyrite framboid formation is proposed. This mechanism requires primary iron sulphide particels to be attracted to one another because of the ferrimagnetic properties of a precursor FeS polymorph or alternatively by Van der Waals forces accentuated by the presence of charged ions in a strong electrolyte. Ordering of resultant microcrysts is mainly a close-packing effect which produces robust aggregates resistant to deformation during subsequent diagenesis. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
