The serpentinizedand/or carbonated ultramafic rocks ofthe Swat valley ophiolite locally contain accessory to trace amounts of microscopic to rnegascopically visible grains of garnierite. Such grains mostly occur in sampks where the serpentinisation andlor carbonation are rather pervasive and accompanied by supergene alteration. Their optical properties and chemical compositions are extremely variable and differ greatly from spot to spot within individual grains which appear to, be in timate mixtures of different compositions. The highly variable and, in most cases, high to very high concentration of FeO (up to -54 wt.%), and abnormally high CaO contents (ranging up to -3 wt . %) in the chemicalanalyses make them distinctfrom the serpentine vane ties of gurnim'tes reported fiom other localities. Most ofthe gamieriee grains seem to be pseudomorphic after, and contain relic patches of, pentlandite, and might have developed as a result of reaction between the 'normal' matrix serpentine or talc and the original Gagmatic sulfide. As their occurrence alongfrnctures in the rocks is clear at least in some cases, their fornation probably took place after the main episodes . of serpentinisation and carbonation and was probably brought about by the processes of weathering and supergene alteration. The association of calcite with gamierites in some of the rocks indicates that the fluid, which caused the alteration, was charged with calcium and CO, and this fac tor probably also accoun tedfor the anomalously high values ofCaO in the garnieri tes .
[1]
G. Christidis,et al.
Compositional Variations in Smectites: Part I. Alteration of Intermediate Volcanic Rocks. A Case Study from Milos Island, Greece
,
1993,
Clay Minerals.
[2]
G. Brown,et al.
The chemical constitution of clays.
,
1987
.
[3]
A. Manceau,et al.
Heterogeneous distribution of nickel in hydrous silicates from New Caledonia ore deposits
,
1985
.
[4]
D. Bish,et al.
Brindleyite, nickel-rich aluminous serpentine mineral analogous to berthierine
,
1978
.
[5]
G. Springer.
Compositional and structural variations in garnierites
,
1974
.
[6]
M. Fleet,et al.
The Chemical Compositions of Synthetic and Natural Pentlandite Assemblages
,
1973
.
[7]
G. Brindley,et al.
The Nature of Garnierites —I Structures, Chemical Compositions and Color Characteristics
,
1973
.
[8]
G. Brindley,et al.
The Nature of Garnierites — II Electron-Optical Study
,
1973
.
[9]
K. Jasmund,et al.
Synthesis of Mg and Ni antigorite: A correction
,
1972
.
[10]
K. Jasmund,et al.
Synthesis of Mg- and Ni-Antigorite
,
1971
.
[11]
B. Mason,et al.
Pecoraite, Ni6Si4O10(OH)8, Nickel Analog of Clinochrysotile, Formed in the Wolf Creek Meteorite
,
1969,
Science.
[12]
G. T. Faust.
The hydrous nickel-magnesium silicates—the garnierite group,
,
1966
.