118 
Rex T. Prider. 
quartz-magnetite rocks, the original carbonate must have been largely siderite 
with but small admixture of magnesite. The metamorphism has been 
effected under thermal, rather than regional conditions, as evidenced by 
the complete lack of orientation in the amphiboles and orthopyroxenes formed 
dining this period. 
In the case of the quartz-hematite-grunerite rock {&), it would appear 
that limonite was a constituent of the original quartz-carbonate sediment, 
and has, by re-crystallisation given rise to well crystallised hematite without 
any reaction with the quartz. Si02 has reacted only with the (Fe, Mg) 
carbonates to give rise to the grunerite. Such a quartz-limonite-iron car- 
bonate rock is known amongst modern bog iron deposits (Van Bemmelen, 
1900, p. 319). 
The presence of considerable MgO and possibly CaO, and the variable 
proportions of quartz, iron ore, and amphibole (or hypersthene) throughout 
the rock seems to indicate that greenalite cherts were not the sediments from 
wliich the eulysitic rocks were derived, and while the sedimentary origin 
is clear, there is some doubt regarding the original character of the sediment, 
but it appears most probably to have been a banded limonite-iron carbonate 
rock. 
(ii) Calc-silicate rocks . — Xenoliths of this type have only been noted 
in one place (114 chains X., 113 chains E. from datum). The rocks form 
a well defined band in the coarse porphyritic gneiss, rimning parallel to the 
strike of the enclosing rocks. The lime silicate rocks occur in bands and 
lenticles running through a band of white vein-like quartz. 
The rock is similar to specimen 1249 (described earlier), differing only 
in the relative proportions of diopside and grossularite, and in being more 
siliceous. It has the following approximate mineralogical composition 
(Vol. %) 
Quartz 50 per cent, diopside 18 per cent, epidote 5 per cent, grossu- 
larite 25 per cent, amphibole and sjihene 2 per cent. 
Isotropic grossularite is the only idioblastic mineral, and it encloses 
diopside and occasionally quartz. 
Diopside, which is not enclosed by grossularite, is altering to a fine 
fibrous colourless amphibole. 
These rocks undoubtedly have the same origin as the lenticles of lime 
silicate rocks in the lower quartzites. They represent xenoliths of the 
Jimperding metasediments which have been caught up in the intrusive 
porphyritic microcline granite. 
(iii) Co7'dierite-anthophyllite rocks and related types , — -These rocks are 
found in a large xenolith in the granite gneiss at a position 236 chains E., 
177 chains S. from datum. The occurrence is more or less circular in shape 
and about 5 chains in diameter. It consists largely of anthophyllite-hyper- 
sthene-pleonaste rocks, but several other types, viz., cordierite-anthophyllite 
and biotite-clinochlore-anthophyllite rocks are found here. 
These rocks have been fully described elsewhere (Prider, 1940), but 
the cliemical analyses are repeated here in Table 3. The conclusion re- 
garding the origin of these anthophyllite-hypersthene-spinel rocks is that 
they \\'erc‘ derived from a hypersthenite magma contaminated by aluminous 
material. The cordierite-anthophyllite assemblages were developed from 
the spinel hypersthenites during the period of intrusion of the granite gneiss, 
by the addition of silica from the granite magma. 
