A quick, simple modeling exercise suggests that vertical cylindical bodies
exhibit a "flowered" anomaly pattern in their cross-horizontal gravity gradient,
e.g., dGx/dy, but not in their vertical gradients, dGz/dz, or in-line gradients,
dGx/dx, though the latter may be somewhat more laterally extensive than other
patterns. (No big surprise, eh?) Also, the sampling grid I see on the BHP web
page is rather more dense in one dimension than the other, what with 100-m line
spacing and (supposedly) a 250-m effective station interval. Could Misery have
been "missed" for simple sparseness reasons?
--Will Frangos
Ken E Witherly wrote:
> Steve/all:
>
> On the BHP web site at:
>
> http://www.bhp.com/default.asp?page=951#
>
> a profile over a pipe is shown comparing Falcon data with ground data. The
> lateral resolution for Falcon (as shown) is certainly better than 250m
> (maybe some good old predictive filtering?).
>
> I don't see any 'flowering effect' in this example; the anomaly is wider
> than the pipe but simply fits the width of the lake, the other major
> (primary?) source of the observed density anomaly in these lake-pipe duet's
> that are so common in the NWT.
>
> In the text at the top of the same page, there is also discussion regarding
> not seeing a pipe of dimensions 140m by 100m, so there is seems to be a gray
> area as to what can be resolved.
>
> Ken
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On Behalf Of Stephen Reford
> Sent: Tuesday, January 09, 2001 11:42 AM
> To: [EMAIL PROTECTED]
> Subject: Re: [SEGMIN]: But what can it do?
>
> Terry,
>
> Apparently, kimberlite pipes result in a "flower"-type response in the
> parameters derived from the Falcon data that have a much larger dimension
> than the pipes themselves. I understand that BHP detected one pipe with a
> 60 m diameter.
>
> Cheers! Stephen
>
> On Tue, 9 Jan 2001 [EMAIL PROTECTED] wrote:
>
> >
> > In a message dated 1/9/01 6:36:58 AM, [EMAIL PROTECTED] writes:
> >
> > << Based on information that has appeared elsewhere, BHP states as
> acquisition
> >
> > cost for Falcon of ~US$60 lkm (or $15/station since they as well state
> they
> >
> > measure data at about a 250 sample interval). This is about airborne EM
> >
> > comes in at, so is not out of line. However, BHP's right to a 51% interest
> >
> > certainly looks like you've invited the proverbial 800 lb gorilla to
> >
> > dinner >>
> >
> > Sheesh, Ken, I think 250-meter gravity-gradient-sampling is downright
> > terrible for kimberlite exploration.
> >
> > Very few economic pipes on the planet, if I remember right, have surface
> > dimensions in excess of 250 meters. The giants like Mwadi, Orapa, Jwaneng
> > (with grades less than 1 carat/tonne) probably would be nicely imaged with
> > 250-meter gradient-stations. BUT, smaller (less than 20-million-tonne) but
> > high-grade pipes (>4 carats/tonne) like Mir, International, and even
> > Lac-De-Gras' Misery and A-154-South pipes could be trouble for any
> > 250-meter-station technique. Even with the averaging/smearing inherent in
> > airborne geophysical sampling--I'd be worried about "missing" the
> high-grade
> > but smaller kimb target.
> >
> > Comparing line-kilometer costs between HEM and Falcon is similar, but the
> > high (<10-metre) sampling-rate of HEM probably still make it the superior
> > airborne method for my kimberlite exploration programs. I believe Falcon
> > probably has greater exploration potential in oil/gas exploration where
> basin
> > targets/structures are large and shallow density-contrasts are better
> known
> > thanx to 3D-seismic-static-corrections.
> >
> > Thanks for posting the BHP-Falcon promotional stuff, it is always
> > interesting.
> >
> > Best Regards,
> > Terry J. Crebs
> > California Registered Geophysicist
> > Lakewood, CO USA
> >
> >
> >
> > _______________________________________________________
> > List archive: http://www.mail-archive.com/[email protected]
> >
>
> _______________________________________________________
> List archive: http://www.mail-archive.com/[email protected]
>
> _______________________________________________________
> List archive: http://www.mail-archive.com/[email protected]
_______________________________________________________
List archive: http://www.mail-archive.com/[email protected]
