In Kerala, more than 90% of quarries are engaged in granite (building stone) extraction. Often officials engaged in mineral administration as well as mine owners find it challenging to quickly estimate the mineable reserve of granite (building stone) in an applied area. Preliminary or quick estimation of granite (building stone) is necessary for processing applications for mineral concessions. It is the duty of the district geologist to report such estimates to the Director of Mining and Geology. This aids the Director in including the tentative validity of the lease in the Letter of Intent issued.
In the State of Kerala, mining plans for granite (building stone) and
other minor minerals were introduced in 2015, and until then, no importance was
given to correctly estimating the mineable mineral reserve. This has resulted
in a loss of registration fees and stamp duty concerning the registration of
leases. It has also led to the granting of leases for periods longer than they
deserve. For instance, an individual with less than one hectare of land used to
obtain a lease for 12 years.
In 2015, when mining plans were introduced in the state,
there were only a few Recognized Qualified Persons (RQPs) available for the
preparation of mining plans. Geologists new to mining plans found it
challenging to understand the concept of bench mining and the computation of
the volume of mineable and blocked reserves. Some RQPs, also new to mining plan
preparation, submitted plans with exaggerated volumes. Mining plans with 10
lakhs metric tonnes of mineable reserve for one hectare area were observed. Upon
noticing these exaggerated values, the then geologists were warned about them,
and instructions were given to arrive at a tentative mineable reserve by
averaging 3.2 lakhs tonnes per hectare, as mentioned in Form II for processing
lease applications. This value of 3.2 lakhs per hectare was derived in 2017 by
dividing the sum of the annual production of around 250 quarries by the sum of
the lease area. It is worth noting that when this computation was made, the
average lease area was approximately 2 hectares, and there were leases less
than one hectare granted as per the erstwhile KMMC Rules 1967.
Now, the scenario has changed, and people are applying for
quarrying leases for larger areas, some extending up to 15 hectares.
Frequently, RQPs express concerns that certain geologists may show hesitation in approving mining plans when the mineable quantity surpasses the average of 3.2 lakhs/ha outlined in Form II. Similarly, some geologists note instances where RQPs tend to be overly optimistic, recording an excess quantity in their submitted mining plans. Nevertheless, the unrealistic volume estimations may result in the following issues:
Estimating mineable reserve- a ready reckoner
Since mining areas have varied size, shape and topography
and since the mineable reserve is dependent on these factors, there is no easy
way to assess the mineable without accurate survey and detailed bench-wise
computation using cross sectional area method or other scientific methods. Even
the result obtained through cross sectional area method varies from person to
person depending on the expertise and experience. However the following
guidelines, tables and graphs can be refereed
to get an estimate of the maximum mineable reserve for an area having different
length and breadth ratio.
Assessment of topography of the land selected for
quarrying
Influence of topography on mineable reserve is detailed in
the previous paper and a recap of the same is given below:
·
Maximum mineable reserve occurs for a similar
shaped quarry (with same area) when a full mound comes within a quarry that
enables the quarry owner to do top slicing. However, it is difficult to meet
such conditions in Kerala.
·
Second maximum mineable reserve occurs for a
similar shaped quarry when the terrain is flat. Such quarries exists in Kerala
but less in number.
·
In sloping terrain, the mineable reserve will be
less than the flat terrain for a similar shaped quarry (with same area).
·
When the degree of slope increases, the mineable
reserve decreases.
Assessment of shape and length-breadth ratio of the land proposed
for operating a quarry
In Kerala, since the availability of the land for mining is
scarce, often the quarry area will have an irregular shape. Sometimes the shape
is so irregular that makes the quarrying area a feel that the land is not contiguous.
As per Kerala Minor Mineral Concession Rules, a quarrying lease can be granted
for a land that is contiguous and only if the length to breadth ratio is less
than 4:1. The length breadth ratio has been fixed for a reason that, in a land
with higher length to breadth ratio, the mineable reserve will be very less.
Let us examine how the mineable reserve vary with change in
shape for the example of 1 ha given above
The following figure shows 1 ha area in different length to
breadth ratios.
Similarly, the results of 2:1 and 3:1 have been computed for different areas and the results are depicted in the following table:
While computing the reserve following norms were adopted
namely, Specific gravity of granite (building stone) = 2.5, Bench height and
width = 5 m, Terrain = Flat and soil cover = Negligible, Minimum quarry floor
width at UPL= 15 m
These values were mathematically interpolated to draw the
graph of the mineable reserve for various length : breadth.
Result of the analysis
Given same topographic setting, the quantity of mineable reserve
changes drastically with length: breadth ratio. The data for area from 1 ha to
20 ha is summarized below:
From the above data, several
conclusions can be drawn.
·
The table highlights a reduction of 33 to 44
percent in mineable reserves for areas with a length-to-breadth ratio of 1:1 to
4:1. The rate of reduction is more pronounced in smaller areas compared to
larger ones.
·
There is an approximately threefold increase in
mineable quantity when the area is doubled.
·
The relationship between the mining area and the
quantity of mineable mineral reserves is not linear. The quantity does not
increase uniformly with the increase in the area. For example, if the mineable
reserve is 3.03 lakhs for one hectare, it is not 6.06 for two hectares, and it
is not 9.18 for three hectares, and so on.
Important Takeaways:
·
Computation of mineable mineral reserves is
crucial in mineral administration.
·
Mineable mineral reserves depend on guidelines
issued for mining plan preparation. In the context of granite (building stone)
mining, the mineable reserve primarily relies on the topography, size, and
shape of the land where mining is proposed. The mining plan approving authority
should consider all these factors.
·
The existing method of computing mineable
reserves based on dGPS survey and the cross-sectional area method is less
accurate than the latest techniques like Drone-based LIDAR survey.
·
Results from the standard cross-sectional area
method used for present-day computations will be more accurate when bench-wise
computations are performed. The general computation method of multiplying the
cross-sectional area of the quarry with influence yields more reserve than the
actual mineable reserve.
·
There will be a change in mineable quantities
computed by two RQPs provided the same survey data is issued to them. This
means there is a percentage margin for the computed quantity.
·
The relationship between the mining area and the
quantity of mineable mineral reserves is not linear.
It is important to note that the graphs and associated
values provided in this paper should be considered as reference values and not
as real estimates. The purpose of presenting the graphs is to make the mining
plan approving authority aware that the mineable reserve of the area under
consideration for a sloping area shall always be less than the value computed
for a similar area in flat land. The graphs provided in this paper may be used
only as a ready reckoner to quickly check whether the estimate is acceptable or
not.
Annexure: Granite (building stone) mineable mineral reserve estimation chart
Author: Biju Sebastian
Caution:
The data provided in this paper is for regular shaped quarry and not for the usual irregular shaped quarry and hence these data should be used with utmost care. The information provided is only for making general awareness on assessment of mineable mineral reserve in the context of granite (building stone) mines in Kerala. As mentioned in this paper the mineable reserve depends on topography, size and shape of quarry and no two quarries have same topography or size or shape.
Disclaimer:
The information on this website is provided "as is" and "without warranty." In terms of how this information is used or the results of its usage, the author disclaims all liability.
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