Colibri receives assays from core drilling on Colibri Project that confirm coarse gold ("nugget") effect

    Listed TSX-V: CBI

    VANCOUVER, Aug. 13 /CNW/ - Colibri Resource Corporation has received
assay results from 2152 m of diamond drill core on the Colibri Project, Sonora
Mexico. As described in more detail below (see also Tables 1-2 and maps posted
on, drilling intersected multiple anomalous
intervals that returned gold assay values ranging from 25 ppb to 3.08 grams
per metric tonne. Total thickness of these anomalous intervals is 424 m.
Assays from selected anomalous zones indicate that conventional analyses of
crushed samples (less than 150 sieve mesh) systematically underestimate the
gold content of samples. Many samples greater than 150 mesh sieve yielded
markedly higher gold assays than corresponding fine grained powders, an
indication of coarse grained gold ("nuggets") similar to those visible in hand
specimens from local mine dumps and underground mine workings.
    The Colibri Project is held by an option agreement to acquire 100%
ownership of 6564 hectares made between the Mexican subsidiary of Colibri,
Minera Halcones SA de CV, and a private Mexican company. Exploratory drilling
is mostly focused on down-dip and along-strike projections of historical
underground mine workings and targets identified by an Induced Polarization
geophysical survey. Previous reverse-circulation drilling of these targets
during 1994, 1998, and 2005 yielded significant gold mineralization (see News
Release of January 25, 2006; see also Table 1 and drill hole location maps
posted on At San Francisco mine, the 1998 and
2005 drill holes intersected 19 intervals with greater than 500 ppb (0.5 g/t)
gold. These intercepts correspond to different structural levels of a
NE-dipping quartz vein-reverse fault system.
    Three areas were targeted for diamond drilling during the 2006-07 season:
the San Francisco mine, the Naranja Zone and the Nopal Zone (see Table 1 and
drill maps). In this stage, Britton Brothers drilled mostly HQ diameter core
with a few intervals of NQ diameter core. Drilling conditions proved to be
exceptionally difficult and water intensive, with broad intervals of strongly
sheared, fractured rock encountered. Core recovery was generally good,
90-100%. Hematite-flooded breccia or gouge zones with quartz veins and
stockworks are common features of recovered core in all holes. Several holes
were terminated due to difficult drilling conditions in strongly sheared,
brecciated rock (CDH-1, 6, 7)
    Every drill hole cut multiple intervals containing greater than 25 ppb
gold. Table 2 reports assay results for each of these anomalous zones. Initial
assays of crushed samples (less than 100 mesh) yielded gold content greater
than 500 ppb (0.5 g/t) for 11 samples, most corresponding to high grade
targets intersected by previous RC drilling efforts. However, grades of these
core samples were lower than RC results in several cases. Because of the
inability of core drilling to reproduce prior RC drill results, Colibri
suspects a sampling and/or recovery problem in that the core assays do not
report coarse gold or "nuggets". Hand samples collected from underground mine
workings and mine dumps contain coarse, visible gold associated with quartz
and hematite. To test the extent of the coarse gold problem, Colibri analyzed
a second split of samples from 104 anomalous intervals. Additional columns in
Table 2 compare gold analyses between the powdered (-150 mesh) and coarser
(+150 mesh) fractions of these second samples.

    Pertinent results of the diamond drill core analysis are:

    1) Each drill hole intersected broad intervals of disseminated gold
       mineralization in stockwork. The total thickness of recovered core
       with greater than 25 ppb gold is 424 m (20% of the total 2152 meters

    2) Drilling intersected multiple higher grade (500 to 3080 ppb gold)
       intervals associated with shear zones and quartz breccias. The total
       thickness of core returning gold assays greater than 500 ppb (0.5 g/t)
       is 19.1 m.

    3) Tests for coarse gold were conducted on 104 samples, 85 of which
       represent drill intervals with initial assays exceeding 25 ppb gold.
       Of these samples, 29 returned greater than 280 ppb (0.28 gpt) gold in
       the coarser than 150 mesh fraction, compared with lower concentrations
       below 150 mesh, a clear demonstration of coarse gold mineralization.
       Most notable is sample CDH-499 where the greater than 150 mesh split
       of the sample contains 34.88 grams per tonne gold and the finer than
       150 mesh split of the same sample 1.6 grams per tonne gold. When
       combined the complete sample contains 3.08 gpt.

    Other notes on specific target zones:

    1) Colibri is encouraged by results from the Naranja Zone, where drilling
       penetrated the northwest edge of a large geophysical anomaly. Holes
       CDH 6, 7, and 9 returned assays greater than 0.25 g/t gold from five
       intervals located at less than 90 m depth. Hole CDH-7 was terminated
       at a depth of 91.1 meters due to difficult drilling conditions in
       fault gouge containing 0.12 gpt gold. In this area, Induced
       Polarization surveying reveals a coupled resistivity and chargeability
       anomaly within a district of numerous dry placer mining operations and
       artesanal underground mines (see maps posted on Also present in this area is a low-angle
       normal fault (detachment fault), manifested in nearby arroyos by broad
       zones of brecciation and hematite/caliche alteration. This fault zone
       appears to form an undulating surface beneath the Naranja Zone, a
       geologic feature typical of the nearby operating mines and advanced
       prospects of this class.

    2) Results from the San Francisco mine area (drill holes CDH 1-5) confirm
       the presence of anomalous gold within a NE-dipping network of quartz
       veins and reverse faults. Multiple intercepts returning assays greater
       than 0.5 g/t gold provide valuable infill data to integrate with
       results from 1998 and 2005.

    3) Drill holes NDH 1-4 from the Nopal Zone did not reproduce the broad
       intervals of high-grade gold reported from 1994 RC drilling of holes
       NRC 8 and 9 (see Tables 1 and 2). However, one 4.5 m interval of NDH-1
       returned assays between 0.43 and 0.54 g/t gold for powdered samples,
       with one interval of 7.05 g/t for the greater than 150 mesh sample,
       compared with 0.54 gpt for the finer than 150 mesh sample. Numerous
       sheared quartz veins throughout the Nopal zone have yielded high-grade
       rock chip samples (see Colibri Corporation prospectus posted on This vein network is now mapped in detail (see, and merits further sampling and

    Colibri has not completed all tests of samples and is reviewing future
sampling and drilling methods. In comparing the four generations of drill
data, inconsistent results from holes drilled into similar targets are
interpreted to be a manifestation of the nugget effect coupled with intrinsic
heterogeneity of gold mineralization that is a common characteristic of the
operating nearby gold mines. Other factors probably include significant
contrasts between drilling techniques and assay labs, plus chronically poor
sample recovery in intervals of sheared, mineralized rock. Compilation and
integration of results from the different stages of drilling is ongoing.
    Core samples were split on site using a diamond saw. Half of the sample
was logged and stored on site and the other half bagged and delivered to
Sonora Sample Preparatory Lab in Hermosillo, Mexico. Sonora Sample Prep Lab
initially prepared sample pulps consisting of the finer than 100 mesh fraction
of crushed samples. This split was sent to International Plasma Labs (IPL) in
Vancouver. In the second phase of core assays, Sonora Sample Prep sent the
entire crushed sample to IPL. IPL sieved the samples using 150 mesh screen,
then weighed and assayed separately the greater than 150 mesh and less than
150 mesh fractions. Assays were performed by IPL using a standard combination
of atomic absorption and fire assay techniques.
    Exploration was conducted under the supervision of J.J. Irwin, B.Sc.,
Ph.D., the qualified person under National Instrument 43-101 on this project.

    Warrants Update

    Colibri is happy to report that almost all the publicly traded half-share
warrants have been exercised that were due to expire on July 28, 2007. The
additional funds received by the company now results in a cash position
exceeding four million dollars to be spent on the drilling programs that will
be initiated beginning October 2007 at our claim sites in Sonora, Mexico.

    The TSX Venture Exchange has not reviewed and does not accept
    responsibility for the adequacy or accuracy of the contents herein.

For further information:

For further information: Visit our website at or call Lance Geselbracht, P.E., (604) 669-7591

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