Download Carbonatite occurrences of the world: map and database, by AR

JOURNAL OF PETROLOGY
VOLUME 50
NUMBER 1
PAGES 195^196
2009
doi:10.1093/petrology/egn080
Book Review
Carbonatite occurrences of the world: map
and database, by A. R. Woolley and B. A.
Kjarsgaard. Geological Survey of Canada,
Open File 5796; 28 pages, 1 sheet, 1 CD ROM.
$18.45 in Canada; $24 for other countries.
Free download http://ess.nrcan.gc.ca/esic/
geoscan-e.php
Labour of love
For those of us who do not have the genes needed for
sorting, cataloguing, and pigeon-holing, we need those
who do. This open-file report (5796) from the Geological
Survey of Canada entitled Carbonatite occurrences of the
world: map and database includes a CD brimming, perhaps
overflowing, with information about carbonatites. Woolley
started listing alkaline rocks and carbonatites along with
their ages, spatial distribution, and associated rocks types
in his volume on the carbonatites of North and South
America that appeared in 1987. Since then, other volumes
have appeared with Woolley acting as the main driving
force. These volumes catalogued and described carbonatites from Africa, and the former USSR, including details
of location, associated rock types, tectonic setting and ages.
This GSC open file consists of Word, Excel and pdf files
that include: (1) a master file containing brief descriptions
of 527 carbonatite occurrences; (2) a list of references;
(3) an introduction along with several maps; (4) an index
list of all localities; (5) a reference file listing those carbonatites associated with economic deposits. The five Excel
files list: (1) all known carbonatites; (2) carbonatite occurrences of economic interest; (3) extrusive carbonatites
including mantle debris contained within them; (4) silicate
rock associations; (5) an index list of all localities. Maps
include a world geological map with all occurrences noted
(in both hard copy as well as digital format), and 21 maps
contained in the introductory document, most available in
digital form.
In the early days, carbonatites were difficult to recognize
but now, particularly with airborne geophysics, many
more have been identified and this open file documents
527 occurrences. No doubt more will be found. Based on
this recent compilation, Africa still manages to hold the
record (35%), and Asia contains 30% (Russia has been
included in Asia).
We already knew that carbonatites are found on all continents and that most occur in stable cratonic areas, but
now we have substantial confirmation that this is indeed
the case. The introductory document reviews the different
carbonatite^silicate rock associations (now listed as eight),
age groupings (11 in all) and carbonatites of economic
interest, and contains 22 figures (all but one are maps)
showing the localities of carbonatites. Whether all of the
21 maps are needed is a moot point. Figure 8 includes a
map of ‘kimberlite^carbonatite association’ and only five
occurrences are documented, and in Fig. 4 showing the
‘basanite^carbonatite’ association only three are shown.
In the introductory text, the authors have managed,
for the most part, to avoid many of the minefields
associated with carbonatite research, but they do venture
into distinguishing carbohydrothermal from magmatic
carbonatites, an excursion no doubt of interest to many
Russian geologists. A neophyte might ask for the definition
of a carbohydrothermal carbonatite, how such rocks differ
from magmatic carbonatites, and the criteria used to
recognize them. In addition, the introduction tends to be
somewhat choppy and partly muddied by diversions into
discussions that are of interest only to those involved with
carbonatite research. It perhaps would have been better to
leave the introduction as simply an account of the database, how it is organized and what the highlights are.
The authors have wisely avoided any ‘in depth’ discussion in interpreting the findings that emerged from their
compilation. They draw attention to some interesting features, especially the association of carbonatites with a relatively wide range of rock types (including kimberlites), and
the division of carbonatites into 11 age groupings using
data of variable quality. Compiling the ages, 264 in all,
and then dividing them into 11 distinct groups implies
some significance to the temporal evolution of carbonatite
magmatism, and implies events of global significance. A
more detailed discussion of the criteria used to establish
the groupings and the range for each particular group
would have been useful.
This compilation will undoubtedly settle some questions
and it appears that the authors already have a paper in
press that will answer some of these. Questions that immediately spring to mind are: how many carbonatites of
the 527 are spatially associated with silicate rocks, at least
at their present erosion level? How many are dolomitic
carbonatites? How many are contained within Archean
cratons? How many are associated with rifts? Why do
some carbonatites of the same age occur over extensive
areas of the Earth’s crust, such as those in the Kola
Peninsula?
ß The Author 2009. Published by Oxford University Press. All
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JOURNAL OF PETROLOGY
VOLUME 50
How useful is this compilation? Clearly, it is packed with
information but accessibility is not easy. I was forced into
the introduction and then I had to dig myself out to download other files. Unfortunately, there is no direct access
from the main menu into each file. This was something of
a nuisance.
Who will benefit from this package? Certainly the
mining community as well as national and state surveys
will find it useful, not only for providing relatively detailed
information about each complex, but also for assessing carbonatite exploration programmes.
Additional ages, especially high-quality, U^Pb zircon
dates will, no doubt, help resolve whether there are distinct, worldwide events capable of generating carbonatitic
melts, and how many of the silicate rocks are coeval with
their spatially associated carbonatites. It will take some
years before we get this sorted out but now at least we
have a framework. This compilation is a good start.
NUMBER 1
JANUARY 2009
It would be easy, but unfair, to be picky about a detailed
compilation such as this. However, if I were to have one
single criticism about this compilation it would be that it
is not easy to navigate. Given the considerable amount of
time that has been spent on the compilation, some additional work to help make the open file more user-friendly,
more accessible, and better linked would have helped a
great deal. However, this compilation represents a contribution that will be invaluable to anyone interested in carbonatites, and the world map that outlines the global
distribution of carbonatites is especially useful.
Advance Access Publication January 21, 2009
Keith Bell
Ottawa
196