Isotopic dating of rocks and minerals from the pipe give an age of
1.178 billion years. This is the age of the eruption. Isotopic dating of
garnets and clinopyroxene in the diamonds indicated that the diamonds
formed about 1.580 billion years ago. Thus, the diamonds formed in mantle
eclogite and mantle peridotite almost 400 million years before the magma
picked them up and carried them to the surface.
Most of the diamonds at Argyle are resorbed dodecaheda.
A small percent of the diamonds from Argyle are sharp-edged octahedra
with hexagonal surface pits.
Most diamonds are found in kimberlite. The rocks at Argyle are
lamproite. Since the recognition of diamond-bearing lamproite in Western
Australia, lamproite pipes in other areas have become the target of
The morphology of juvenile clasts and the presence of bedded
tuffs, accretionary lapilli, and water escape structures indicated that
the Argyle diatreme formed from several
eruptions. The explosive eruptions were caused by the interaction of
lamproite magmaand shallow groundwater. Cross-section of the Argyle
diatreme from Boxer and others (1989).
Diamond exploration in the Kimberley and the difficulty in determining
the grade of ore in diamond pipes are described by
Most diatremes, like those in the
Navajo volcanic field,
do not contain diamonds. Most young diatremes have maars or tuff cones
at the surface like
respectively. The surface features of many diatremes in Australia have been eroded away.
Diamonds in Crater of Diamonds, Arkansas
are hosted in lamproite but the diamond content (0.5 carat per 100 tons) is not economical for mining.
Sources of Information:
Boxer, G.L., and Jaques, A.L., 1990, Argyle (AK1) diamond deposit,
in Geology and Mineral Deposits of Australia and Papua New Guinea,
Hughes, F.E., ed., The Australian Institute of Mining and Metallurgy,
Boxer, G.L., Lorenz, V., and Smith, C.B., 1989, The geology and
volcanology of the Argyle (AK1) lamproite diatreme, Western Australia, in
Kimberlite sand Related Rocks, Vol. 1, Their Composition, Occurrence,
Origin and Emplacement (Eds J. Ross and others), geol. Soc., Aust. Spec.
Publ. No. 14, p. 140-152.
Jaques, A.L., Haggerty, S.E., Lucas, H., and Boxer, G.L., 1989,
The mineralogy and petrology of the Argyle (AK1) lamproite pipe,
Western Australia, in Kimberlites and Related Rocks, Vol. 1, Their
Composition, Occurrence, Origin, and Emplacement (Eds. J. Ross and
others), Geol. Soc. Aust. Spec. Publ. No. 14, p. 153-169.
Jaques, A.L., Lewis, J.D., and Smith, C.B., 1986, The kimberlites
and lamproites of Western Australia: Geological Survey of Western
Australia Bulletin 132, 268 p.
Jaques, A.L., Lewis, J.D., Smith, C.B., Gregory, G.P., Ferguson,
J., Chappell, B.W., and McCulloch, M.T., 1984, The diamond bearing
ultrapotassic (lamproitic) rocks of the west Kimberley region, Western
Australia, in Kimberlites I: Kimberlites and related rocks, edited by J.
Kornprobst: Amsterdam, Elsevier, p. 225-254.