Replies to post #153697 on KAT Exploration Inc (KATX)

[ShortonCash]

Still holding out for a Rusty Ridge IOCG announcement...

In a typical vertically zoned IOCG system, magnetitedestructive,
hematite-rich hematite-sericite-chlorite-carbonate
(HSCC) alteration dominates upper levels, whereas magnetite-rich
alteration (potassic at intermediate depths, grading into deeper
sodic or sodic-calcic alteration) dominates at depth. Thus the current
erosion level determines whether the exposed or near-surface
portions of the system are hematite-rich or magnetite-rich. If the
level of exposure is sufficiently deep, overprinting magnetite-rich
potassic alteration tends to be more focussed around the deposits,
enhancing the magnetic highs. On the other hand, if upper levels of
the system have been retained, magnetite-destructive hematite-rich
alteration hosts the mineralization. In this case the signature is
a relatively smooth pattern, which can be a local magnetic low
(depending on the host rock magnetization) within the overall
broad high associated with deeper and/or more laterally extensive
magnetite-dominant alteration. Tilting of a vertically zoned system,
or upfaulting of the deeper magnetite-rich portion, may juxtapose
the magnetite and hematite zones, producing juxtaposed, rather
than ”coincident” gravity and magnetic anomalies.
High grade regional or contact metamorphism of hematiterich
zones can impart an intense thermoremanence to the hematite,
which can cause large magnetic anomalies. This appears to explain
the strong magnetic anomalies exhibited by massive hematite bodies
of the Mount Woods Inlier that have been contact metamorphosed,
such as the Peculiar Knob deposit (Schmidt et al. 2007),
whereas similar unmetamorphosed massive hematite at Prominent
Hill produces no discernible magnetic anomaly.
At continent to province scale favourable tectonic settings for
ancient deposits may be recognisable from regional potential field
data sets, supplemented by seismic, magnetotelluric or other deeppenetrating
methods. Ancient buried subduction zones are characterized
by arc-parallel linear belts of magnetic highs, corresponding
to magnetite-series granitoid provinces, and lows, corresponding
to ilmenite-series granitoid provinces or sedimentary basins.
Subduction-related magnetite-series belts are much more prospective
for IOCG and porphyry copper-(gold) deposits. Belts of reduced,
ilmenite-series granitoids are prospective for Sn-(W) and
also for intrusive-related Au and reduced porphyry Au-(Cu) deposits.
Within belts of magnetite-series granitoids, Cu-Au is associated
with more magnetic magmatic-hydrothermal systems than
Cu-Mo; W-Mo-Bi and Au in tin provinces is much less magnetic.
In oxidized Au-bearing systems, Au mineralization is often associated
with the felsic end of magmatic evolution and is then associated
locally with a weaker magnetic character and higher radioelement
contents. Continental rift settings, which are also prospective
for IOCG deposits, may be associated with rift-parallel regional
gravity and magnetic highs along the ancient continental margin,
with a quiet magnetic zone outboard of the regional highs and relatively
busy magnetic patterns inboard of the margin (Gunn 1997).

core2.gsfc.nasa.gov/research/purucker/purucker_clark_iaga_review_2010_v2.1ed.pdf