Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an improved method
and apparatus for geochemical exploration for mineral,
hydrocarbon and geothermal deposits, and in particular
to an improved method of collecting and processing geo-
chemical samples prior to the analysis thereof.
In conventional geochemical prospecting, samples
of rock, soil, vegetation, stream sediments or water are ~ -
collected and such samples are analyzed for pre-determined
elements for the purpose of revealing anomalous geo-
chemical distributions of such elements, related to
mineralization or the existence of hydrocarbon deposits.
Commonly, the samples are taken in 50il at depths of
between about 10 cm. - 1 m. W~en samples are taken
nearer to the surface, it is usual to discard the top
1 or 2 cm. layer of the soil on the theory that the very
surface may be contaminated to some extent, due for
example to the presence of animals or deposition of
wind swept material. In addition, the collection, storage
and analysis of a large number of samples is very time
consuming and expensive, so that at present it is
practical to take samples only at fairly wide spaced
intervals. As a result, it is often difficult to assess
the significance of some apparent geochemical anomalies.
The present invention relies on the fact that
the earth's surface and to some extent the ocean's surface
is covered with a micro-layer of particulate material in
contact with the atmosphere that is composed of a mixture
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of organic and inorganic constituents. It has been
found that such particulate material reflects the geo-
chemistry of the underlying soils, and when collected
in an appropriate size fraction can provide useful
geochemical information. It has also been discovered
that coarse particulate material occurring on the
surfaces of vegetation and having à biological origin,
also exhibits a chemical composition that is closely
related to the geochemistry of the underlying soils.
Furthermore, the surface particulate material lying on
soils and vegetation is in contact with the atmosphere
and as a consequence, is exposed to oxidation, weathering
and micro-biological phenomena that are unique to the
atmospheric interface. These phenomena provide certain
characteristics that can give high sensitivity in the
detection of gaseous fluxes rising from underlying
mineralization and hydrocarbon accumulations.
, In the present inventlon, particulates which
are contained in the very surface, or surficial layer
of the earth r or of vegetation, or water are collected
and analyzed. Samples of the surficial layer are taken
rapidly, in quick succession, and at relatively low cost.
More particularly, particulate or finely divided material
comprising the surficial layer of soil, vegetation or
water, such as mineral grains, clay minerals, saline
evaporative residues, plant fragments, micro-organisms
and the like are sampled, for example by applying suction
to a tube positioned near to the surface to be sampled.
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It was previously considered that the preferred
range of particle size was between about 50 - 200 microns.
A particle of about 200 microns in size is considered to
be giant, and heretofore it was not considered practicable
to collect particles much larger than about 200 microns
in size. However, it has now been discovered that giant
particles apparently of biological origin are often present on
the surfaces of vegetation and they have been found to
possess chemical compositions which are closely related
to the geochemistry of underlying soils. In addition,
giant particles have been found to be particularly useful
- in wind swept semi-arid regions where fine particles tend
to migrate considerable distances and hence tend to make
the measurements more diffuse than they would otherwise
be. Analysis of such particles heretofore has been a
serious problem, however, especially when such particles
are stored on a tape, considering that the analyses must
be carried out quickly, at low cost, and with good
accuracy.
It has now been found that such giant particles
may be analysed with good accuracy by crushing the par-
ticles prior to their analysis, while they are on the
tape, until their size has been reduced sufficiently to
acilitate their analysis. It has been found that a
vibratory tool applied to the particles for a few seconds
is effective to reduce the particle size roughly by a
factor of about 10 to 1, and the sample is rendered
more homogeneous as well.
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In the arawings,
Fig. 1 is a diagrammatic view showing a
helicopter equipp`ed with a suction tube in accordance with
a first embodiment of the invention,
Fig. 2 is a plan view showing in greater detail
the outer end of the tube shown in Fig. 1,
Fig. 3 is a diagrammatic view of a preferred
form of apparatus for storing collected particulate
material,
Fig. 4 is a plan view showing a portion of
tape used with the embodiment of Fig. 3,
Fig. 5 is a diagrammatic view showing a tape
on which parl:icles have been deposited, being separated
from a cover tape and then being fed past a crushing
apparatus,
Fig. 6 is a side view of the crushing apparatus
shown in Fig. 5,
Fig. 7 is an enlarged side view of a vibrator
transformer used in the crushing apparatus of Fig. 6,
and,
Fig. 8 is a diagrammatic side view of a cyclone
separator which may be used to separate fine and coarse
particles.
Referring to the drawings, and in particular
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to Fig. 1, apparatus for collecting geochemical samples
is shown installed in a helicopter 10. A vacuum pump
sampling assembly 11 is supported on shock mounts in
the back of the helicopter 10 and is connected to a
strong flexible tube 12 which preferably is made of filament
wound glass fibres embedded in epoxy resin, of a length of
about 8 - 10 meters, and a diameter of about 3 - 5 cm. The
tube 12 is relatively stiff but is sufficiently resilient
that it wili yield when it hits an obstruction. The tube 12
terminates in a removable perforated sleeve 13 having a closed
outer end as shown in Fig. 2. The sleeve 13 serves the func- `
tion of sieving out leaves, twigs, etc. and it is formed
of a tough, resilient synthetic resin that is resistant to
abrasion, such as polycarbonate. It is advisable to form
the connection between the tube 12 and the sleeve 13 in such
a manner as to facilitate rapid replacement of the sleeve 13.
The length of the sleeve 13 is about 1 meter. Particulates
sucked through the perforations in the sleeve 13 are fed up
the tube 12 inside an inner suction tube (not shown). The
particulate9 reaching the upper end of the suction tube are
generally below about 600 microns in size, the maximum size
being a function of the size of the openings in the sleeve 13,
and the amount of suction applied to the suction tube. Lar-
ger particles could be passed up the suction tube by in- -
; creasing the suction appropriately, but at present there
does not appear to be any advantage in collecting particles
larger than between about 400 - 600 microns in size.
The inner end of the suction tube is connected to a
cyclone separator 40 as shown in Fig. 8 at an inlet 41. A ~ -
sieve 46 in the inlet 41 blocks particulates belaw about 1000
microns in size. The air containing the particulates spins
around inside the cyclone 40, and the fine particles are
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separated from the coarse particles by means of a
conical mesh sieve 42 inside the cyclone 40 which
preferably is plated with rhodium for abrasion resis- -
tance. The coarse particles decend by gravity to
outlet pipe 43, and the fine particles are discharged
through outlet pipe 44. Excess air leaves the cyclone
40 via outlet pipe 45. The size of the openings of
the conical mesh sieve 42 determines the particle
size separation. In some areas where there is little
wind blown material on the surface, particles above
about 50 microns are retained for analysis; in other
areas where there is significant risk of contamination
by wind swept fine particles, particles above about
200 microns are retained for analysis. The particles
emerging from the pipe 43 are the ones which are
retained; the fine particles emerging from the pipe 44
are discarded. The pipe 45 is connected to a vacuum
pump (not shown) which provides the necessary suction
for removing the particles from the surface of the soil
or of vegetation, for transporting the particles up the
suction tube, and for operating the cyclone 40.
The sampling assembly 11 is shown in Fig. 3
and it consists of a vacuum pump 14 which is connected
to an inertial impaction device 15 which in turn is
connected to the cyclone outlet pipe 43 by means of a `
pipe 16. The impaction device 15 is similar to that
shown in United States Patent No. 3,868,222 of A. R. -
Barringer. Air in the pipe 16 carrying particulates is
directed through the jet 15a against the surface of the
tape 17 the outer surface of which is preferably coated
with a suitable adhesive material such as silicone adhesive.
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The tape 17 is supported by a block 18 to which
is fixed a numbering device which prints a location mark 30
and a number on the tape 17 each time the tape 17 is
incrementally advanced. A supply of tape 17 is carried on
a reel 19 which feeds the tape 17 past the inertial impac-
tion device 15 onto a pickup reel 20. The adhesive
surface of the tape 17 is covered with a cover tape 21
from reel 22. Tape 21 is made of a suitable plastic
material which will not adhere strongly to the adhesive
surface of the tape 17, such as that sold under the trade
mark Teflon. The cover tape 21 protects the particulate
samples prior to analysis.
The samples are collected as circular spots 23
on the surface of the tape 17 as shown in Fig. 4 and the
tape 17 may be advanced incrementally at equal time
periods such as every 10 seconds or equal distance inter-
vals of traverse as determined by distance measuring
equipment on the vehicle 10.
A small microphone may be attached to the
tube 12 to enable sound levels in the tube 12 to be
monitored by the helicopter pilot. By this expedient
it is possible to sense when the tube 12 is banging on
the ground and/or on vegetation. This arrangement,
together with a radio altimeter enables the pilot to
obtain a feeling of the performance of the suction
system and to maintain appropriate flying height.
Instead of being dragged along the ground, the
tube 12 may be drawn across a canopy of trees or of low
growing scrub vegetation whereby particulate material
carried on the surface of the vegetation is drawn into
the sampling assembly 11 through the suction tube.
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This particulate material comprises organic material
derived from the vegetation and contains elements which
are indicative of the nutrient elements in the soil in
which the vegetation is growing. Thus the method has
utility in the exploration of heavily forested regions
and other vegetated areas which are difficult to traverse
by land vehicles.
It will be understood that although the method
of the present invention has been described with reference
to a helicopter, the collection apparatusl suitably
modified, could be installed in a land vehicle such as
a truck or even on a back pack for use by a person on
foot. In the latter case, power for the suction pump
could be provided by a small gasoline engine.
Prior to the analysis of the particles on the
tape 17, the particles are crushed in order to reduce
the size of the particles below about 100 microns and
preferably below about 50 microns, ideally in the range
between about 10 - 30 microns. This is accomplished by
the apparatus shown in Fig. 5, wherein the tape 17 i5
shown being unwound off a storage reel 24, fed past a
crushing apparatus 25, and then wound up on a take-up
reel 26. The cover tape 21 is unwound onto a take-
up reel 27 upstream of the crushing apparatus 25. A ;
small lamp 28 and a photodetector 29 are positioned in
optical alignment on opposite sides of the tape 17, such
that the light emanating from the lamp 28 is interrupted
by the location marks 30 previously printed on the tape 17.
The electrical pulses thereby produced by the photodetector
29 are used to control appropriate circuitry (not shown)
which causes the motion of the tape 17 to stop with the
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spots 23 in proper alignment between hammer 31 and anvil
32 of the crushing apparatus 25. The tape 17 is shown
in Fig. 5 as having a pair of spots 23 at each incremental
location on the tape 17, as for example in the case where
the particulates were collected in the atmosphere rather
than the surface of the earth, using the method disclosed
in U.S. Patent No.-3,970,428 of Anthony R. Barringer
dated July 20, 1976. Generally only one spot 23 of
particulates is present at each location on the tape 17
when processing surficial particulates, but of course an
additional spot 23 could be formed at each location, to ;
be retained perhaps for future analysis. ;~
Each hammer 31 is formed with a head that is
slightly larger than each spot 23, allowing for small
alignment errors, and the hammers 31 as shown in Fig. 6,
are reciprocally driven up and down against the anvils
32 by vibrator transformers 33 which respectively are
coupled to the hammers 31 by connecting links generally
indicated at 34. The vibrator transformers 33 are
adjusted to a convenient frequency, for example 60 I~z.
so that the hammers are applied to the spots with a
frequency of 60 blows per second. The force of the
hammers is adjusted so that the desired amount of crushing
is achieved within a reasonable period of time, e.g. ~-
4 - 6 seconds. A force of between about 6 - 8 kg. is
typical. With such parameters, the particle size is
reduced by a factor of roughly 10 to 1, and the particles
are crushed into fragments which are smaller than about
100 microns in size, or preferably below 50 microns. A
range of 10 - 30 microns is ideal for the laser analysis
method referred to below. After the desired amount of
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crushing has been achieved, the tape 17 is advanced about
half-way between two sets of adjacent spots 23 on the
tape and the hammers 31 are again activated, this time
against the adhesive coating on the tape 17 since the
hammers 31 are now positioned midway between two sets of
adjacent spots 23. This serves to clear the hammers 31
thus reducing the risk of contamination when the hammers
31 are again applied to the next set of spots.
As the tape 17 proceeds incrementally past the
crushing apparatus 25, a new cover tape 35 is applied to
the tape 17 from a reel 36, and the tape 17 with its new
cover tape 35 is then wound up on the storage reel 26
and retained for subsequent analysis.
Several alternative methods of analysis of the
particulates on the tape can be employed. A preferred
method is disclosed in pending Canadian Application
SN 277,443 filed April 29,1977 of Anthony R. Barringer
wherein the particles are volatized by an intense laser
beam and then the volatized matter is excited by a plasma
to prepare the matter for spectroscopic analysis. Alter-
natively, other methods such as X-ray analysis and wet
chemical techniques may be employed, although these latter
methods at present respectively are not as sensitive or
as efficient as the laser method referred to above.
In addition, some of the more easily volatized elements
and compounds may be analyzed by heating the particulates
to drive off the elements or compounds of interest and
then analyzing such elements or compounds, for example
by using apparatus as shown in U.S. Patent No. 3,8G8,222
of Anthony R. Barringer.
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The laser analysis method referred to above
requires very small amounts of material for each deter-
mination, e.g. 5 - 10 micrograms or even less. However,
it is advantageous to collect enough particulate matter
(e.g. about 100 micrograms, more or less) so that the ~ -
adhesive on the tape becomes saturated with particles,
i.e. additional particles will not stick to the tape.
In such circumstances, the amount of particles collected
in each sample will approximately be the same, thus
providing a rough degree of normalization for the sub-
sequent analysis.
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