Rhodolite,
To answer a few of your questions,
- Spinifex texture is generally related to lava flows of at least high-magnesium basalt composition. The texture forms via cooling of the liquid lava in contact with the sea water; the crystals of olivine (or in this case, most likely pyroxene) grow into a needle like habit at the top of the flow, below the pillow textured top.
- peperite is another texture associated with submarine volcanic lavas / intrusions. In this case it is formed by the lava / magma intruding into wet, unconsolidated sediments, where the heat of the intruding magma causes brecciation and often boiling and physical mixing of the liquid magma with the sediment oozes and muds.
Peperites infer subvolcanic intrusions and sills (sills are intruded flat, along the bedding plane of the sediments), whereas spinifex infers a lava flow on the sea floor. I'm not sure it's necessarily a big deal, but if you consider the Besshi VMS model, the VMS forms in proximity to sills. The intrusion of the hot magma into the sediments causes hydrothermal circulation, drawing the goodies (sulphur, metals) out onto the seafloor.
- Regarding pyrrhotite and the magnetism and IP, this is an interesting area. Pyrrhotite is paramagnetic, and conductive. It often shows a magnetic anomaly in large bodies, and because it's conductive, it responds to IP and DHEM.
It is a reduced iron sulphide, which you do find in the root zones of magmatic hydrothermal systems. Note that it's not diagnostic of VMS's, because it's also found in reduced high-termerature environments....like subvolcanic sills, magmatic nickel, etc.
The determination THX would have made as to the prospectivity of the pyrrhotite would have been based on where it was, and whether it was associated with copper anomalism. If you find pyrrhotite in a dolerite dyke, far from sediments, and the dyke isn't altered, then it's not going to make you think you are in the root zone of a VMS system.
Also, not all VMS systems will have pyrrhotite in the root zone, or it may not be preserved. One thing to bear in mind is that mineral systems are long-lived, episodic, and can be siutes for later fluid flow which can wash out or destroy what you'd ordinarily expect to find in the model and, it's only a model - not all women are Elle Mcpherson and not all VMSs exhibit all features of the model. Therefore, absence or presence of pyrrhotite doesn't infer by itself the absence or presence of a VMS.
In all of this you are relying on the THX geo's to, firstly, observe the textures and mineralogy of the drill returns (chips or core), make an inference about the paragenetic information that the pyrrhotite gives, and weigh this against the idealised 'model' - or in some cases, recognise a variance to the model and explain it away so that the prospectivity remains.
The real skill is avoiding confirmation bias and other logical traps which either lead you to say things like "woot, here's pyrrhotite, we must be in the root zone!" or "this pyrrhotite is near some spinifex, our volcanics are all wrong for our model, we need to leave".
Without seeing the totality of the data, I can't comment, except to say that on this website I see a hell of a lot more of the former from commentators who take tidbits of information off the announcements, read a few websites, look at an idealised model of a VMS, and draw an incredibly long bow to claim that every company exploring this region is one drill hole away from the next DeGrussa.
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Thanks heaps!
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