Classification - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 78

WEST KIMBERLY (Lamproite)
WEST KIMBERLY (Ol Lamproite)
SMOKY BUTTE
LEUCITE HILLS
MURCIA-ALMERIA (M-A)
KAMAFUGITES
GROUP II KIMBERLITES
ROCCAMONFINA
VULSINI
VICO

WKL

SB G2K

0.90

WKOL

LH

VULSINI

0.80

R

0.70

M-A

VICO

0.60

KAMAFUGITES

0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90

Niggli Mg

Fig. 3.8 Niggli parameter diagram for diverse potassic rocks. Lamproite data from West
Kimberley (Jaques et al. 1986), Smoky Butte (Mitchell et al. 1987), Leucite Hills (Carmichael
1967; Kuehner 1980), Murcia Almeria (Fuster et al. 1967; Venturelli et al. 1984). Data for

kamafugites from Gallo et al. (1984), Peccerillo (1985), Roman province high potassium leucitites
(Appleton 1972; Cundari and Mattias 1974; Holm et al. 1982, after Mitchell and Bergman 1991)

-

' ' ' '

Australia have higher than the lamproites from Noon-

kanbah, Leucite Hills and Smoky Butte. While studying the K-rich rocks from the
Aldan shield, Bogatikov et al. (1985) made a classi

mg and lower Niggli k

cation of these rocks on the

basis of K mg - SiO 2 parameters (Table 3.1 ).

The classification of lamproite series on the basis of simply K mg - SiO 2 diagram is
quite arbitrary (Mitchell and Bergman 1991). According to this classi cation the

term lamproite is restricted to only the ultrabasic members of the series and does not
follow the modern scheme of classi

cation based on mineralogy.
According to Rock (1987) lamproites were emplaced under volcanic to sub-
volcanic conditions as they have leucite, otherwise they have compositions similar
to those of lamprophyres. They also have a unique paragenesis in that they include
K-richterite and priderite (Wagner and Velde 1986). Lamproites are also charac-
terized by Ti-rich silicates and oxides, and do not have plagioclase. The presence of
a feldspathoid (leucite or analcite or pseudoleucite) is often observed in the lam-
proitic rocks. Inclusion of leucite and elimination of glass in the aforesaid classi-

fication has been advocated by Mitchell (1985).
These rocks are de nitely peralkaline or close to paralkalinity (Wagner and Velde

1986) as evidenced by the presence of normative acmite in the CIPW norm and are
accompanied by alkali metasilicates. They are Mg-rich, and their CIPW norms show
20 % normative enstatite (or diopside) with or without forsterite. There is positive
correlation between K 2 O and MgO. Wegner and Velde studied lamproites from