Geology Reference
In-Depth Information
Table 3.1 Classi
cation and characteristics of rocks of the lamproite series (Modi
ed after
Bogatikov et al. 1991)
Rock types
Rock family
SiO
2
(wt%)
K
2
O (wt%)
K
mg
Olivine lamproite
Ultrabasic alkaline
picrite
38.8
-
41.0
1.6
-
5.1
78
-
89
Madupite
Alkaline
ultrabasic-foidite
41.9
43.6
5.1
8.0
70
80
-
-
-
Wolgidite
Alkaline basic
foidite
43.5
50.5
8.2
11.6
-
-
73
-
77
Jumillite
Alkaline basic
foidite
44.4
-
49.0
2.8
-
7.4
66
-
85
Wyomingite, orendite and
cocite
Alkaline basic
phonolite
48.9
-
51.7
4.1
-
11.0
60
-
83
Fitzroyite, cedricite
(Phlogopite leucitite)
Alkaline phonolite
51.0
59.0
8.6
12.6
55
80
-
-
-
Cancalite
Alkaline trachyte
51.8
57.4
7.7
10.0
67
85
-
-
-
Verite, fortunite
Subalkaline-
trachyte
53.0
-
59.0
3.4
-
9.1
65
-
80
various localities, and observed that in lamproites, the K
2
O content varies between 3
and 7 wt% and may be as high as 12 wt% in extreme cases. The TiO
2
content is
variable and can be as high as 7wt%. Aglassy texture is observed in case of lamproites
from southern Spain, Smoky Butte and Leucite Hills (Wagner and Velde 1986). In
case of Australian (Prider 1982) and Damodar Valley lamproites (Gupta et al. 1983),
the spinels are usually chrome-rich. In the lamproites from southern Spain, Sisco
(Corsica), Moon Canyon, Shiprock and Smoky Butte (all from the U.S.A.) and West
Kimberley (Australia), the F and Cl (0.2 and 0.4 wt%) contents positively correlate
with high K
2
TiO2. MgO and TiO
2
. This suggests the predominance of Ti-rich phlogopite
present in these rocks.
Lamproitic rocks should have the following characteristics (Wooley 1987): 1. They
should have molar K
2
O/Na
2
O> 3 (i.e. they are ultrapotassic) 2. The molar K
2
O/Al
2
O
3
ratio is usually >0.8 and more commonly >1 but below 3. The molar (K
2
O+Na
2
O)/
Al
2
O
3
ratio should be typically >1 (i.e. they are peralkaline). The mineralogy of dif-
ferent types of lamproites is discussed below:
Olivine, chrome-diopside, titaniferous phlogopite, and small amounts of leucite
are the characteristic minerals of jummilites (Borley 1967). Kataphoritic amphibole
(a type of K-richterite) is also present as an interstial mineral. A jumillite from
Mauricia, Spain is constituted of 34 % leucite, 14 % clinopyroxene, 17 % olivine
and 35 % (all in vol%) accessary minerals, which include titanomagnetite, ha
ΓΌ
yne,
zeolite, apatite, etc.
Olivine and phlogopite with small amounts of leucite are the essential minerals
of a verite. Potash feldspar may or may not be present. Calcite is often present as an
accessory phase. Type localities of jumillites and verites are Mauricia and Almaria
provinces of Spain.
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