112
where :
D
k
= diamond
content in kimberlites, mg/m
3
p = average weight of diamond crystals in the studied pipe, mg
Xe= xenolithes in kimberlites in %%
Beside that another formula was deduced for determining the factor of quality
of diamond crystals ( FQ
d
):
_______
DD
Ti
(n)
3
√Pc . Ti
k
FQ
d
= -----------------------------------
2 DPC ( Fe – Ti
k
) Ti
m
where :
FQ
d
= quality factor
of diamond crystals
DD
Ti
(n)
= titanic degree of differentiation the kimberlite melting
Pc = amount of polycrystalic aggregates of diamond in %%
Ti
k
= content Ti in kimberlite in weight %%
Ti
m
= an average content Ti in the mantle rocks ( 0.036%)
Fe = content Fe in kimberlite in weight %%
DPC = degree of preservation
the diamond crystals
Another important factor of diamond potential is a degree of graphitization
(DG), which is expressed as:
1
DG = ----------
DPC
The rate of the pressure drop in a magmatic system is determined using the
amount or percentage of polycrystalline diamond aggregates (P
a
), which is used
as a measure of the rate of change of thermodynamic parameters. The relative
quantity of polycrystalline diamond aggregates (QP
a
) can be used as a measure of
the favorability of thermodynamic regime during the period of diamond
crystallization. The indication of the facial factor of the quality of diamonds (FQ
a
)
can be expressed by following equation
__________
/ 1
FQ
a
= f [ DD
Ti’
3
√QP, ------ ]
DPC
Most diamond crystals are characterized by the ability to luminescence under
ultraviolet light or x-rays. The main colors of luminescence are blue, yellow and
green. More rarely orange and red-pink colors are detected; they are referred to as
“others”. Sometimes a significant percentage of diamonds is characterized by
indefinite (white) colors of luminescence or have no detectable luminescence. An
equation for calculation of the luminescence indicator for diamonds (LID) is shown:
113
________
100 x ( y + / others / ۰ √(b + 0.5 g
LID = --------------------------___________
y + 0.5 others + √ (b + 0.5 g )
Where :
y = the percentage of diamonds with yellow luminescence
b = the percentage of diamonds with bluish luminescence
g = the percentage of diamonds with greenish luminescence
others = the percentage of diamonds with “others” colors of
luminescence
By using the data from 37 kimberlite pipes from Yakutian the dependence
between LID and CPD has been established with a positive correlation
coefficient of + 0,66
-
+0.09. It is suggested that the diamond potential of a
lode source (CPD) can be assessed using the luminescence of diamonds (LID)
obtained from panned samples
and placers.
The research of the factors of diamond-bearing kimberlites has opened the
opportunity to assess diamond-bearings without taking huge-volume probes, but
rather using several chemical analyses of kimberlites and the data of diamonds
morphology from the near river placers to calculate the upper limit of the weight
contents of diamonds in this body. By multiplying the resulting meaning on the
price for 1 carat one can receive the forecasted cost of diamonds in 1 m
3
of that
kimberlite body. The information on the pipes' size in the cross-section allows to
calculate its probable volume and then to forecast estimation of total reserves
and cost of diamonds in that kimberlite pipe. These calculations have been done
and found the verification on the elaborated kimberlite pipes and fields of the
Yakutian province (M.A.Krutoyarskiy, 1968; Milashev, 1984).
9. FACIAL CONDITIONS OF SAFETY DIAMOND CRYSTALS
IN ULTRAMAFIC ROCKS AND KIMBERLITES
Diamond crystals are exceptionally stable mineral under a various
thermodynamic conditions, because the temperature of melting of diamonds
reaches 3570
o
C at the absence of oxygen. The diamond starts transforming in
graphite at the pressure 4.8-3.3 GPa and temperature less 1300 – 900
o
C also
at the absence of oxygen (Figure 11). Therefore, the crystals of diamond are
preserved at considerable rate without free oxygen, if the original ultramafic
or kimberlite melt are comparatively rapidly elevated to the terrestrial
surface.