Assessment of fracturing and blockiness of the Pshenychne gabbro deposit massif

Proper development of the deposit and the choice and use of effective technologies for block stone extraction are impossible without evaluating the structural indicators of the massif. It consists in studying the propagation of cracks in the array, orientation of the main crack systems, studying the anisotropic properties of stone, and predicting the yield of commercial stone blocks in the deposit. This allows both to increase the efficiency of block extraction and to reduce the loss of stone during its extraction, which increases the economic performance of field development. The assessment of fracturing and blockiness of the Pshenychne gabbro deposit was carried out based on the results of studying the core documentation of 11 exploration wells and the documentation of a pilot production quarry. Rose diagrams, pie charts, and fracturing plans were constructed in isolines, and crack systems common in the field were identified.


Introduction
For post-war reconstruction, Ukraine needs both financial and material resources, in particular construction materials.Not the last place here belongs to natural facing stone, which requires further exploration, geological and economic assessment, design and development of facing stone deposits.Zhytomyr region has the largest number of deposits of facing stone in Ukraine, in particular deposits of granites, gabbro, labradorites, confined to the Korosten Pluto of the Ukrainian Crystal shield.
One of the main characteristics of a natural stone deposit that determine its economic efficiency is the fracturing and blockiness of the mineral array.The fracturing of the deposit, in particular the system of common cracks, their directions, angles of incidence and frequency, determines the maximum yield of natural stone blocks from the massif, their size and, accordingly, the commercial value of 1 m 3 of the block.The results of studying the fracturing of the array are used when choosing a method for preparing block stone for extraction, justifying the technology parameters, and creating equipment complexes for extracting and processing blocks.They allow determining the optimal location of the mining front and the direction of its movement relative to the fracturing developed in the massif, increasing the yield of blocks from the massif and reducing stone waste when processing it into products.
Indicators of fracturing of arrays are initial relative to blockiness and determine it.Natural structural blocks are three-dimensional elements of the array structure, cracks are planar, and system cracks are ordered, and non-system cracks are disordered elements of the structure.Blockiness (or percentage of block yield) is a theoretically possible output from an array of stone blocks that meet the requirements of the industry; it is determined by the conditions of occurrence, the fracturing system of the array, the IOP Publishing doi:10.1088/1755-1315/1319/1/012009 2 rock texture and the development system.Data on the possible output of blocks both from the deposit array and from its individual sections should be available to assess the technological suitability of the deposit rocks, design and planning of mining operations.
The classical study of fracturing was performed by H Cloos and R Bolk [1].M M Anoshchenko, L I Baron, M T Bakka, B P Belikov, V O Bukrynskyi Yu H Karasov and many other scientists were engaged in further study of fracturing and blockiness of massifs of facing stone deposits.Their work was used for further research on improving the technology of stone mining.M T Bakka [2], R V Sobolevskyi [3][4] and V V Korobiichuk [2,5] investigated the regular distribution of crack systems in massifs of facing stone deposits.The relationship of fracturing with structural features of gabbroidic arrays was studied in the works of A O Kryvoruchko [2][3]6], S S Iskov [1,3] and V V Kotenko [7], in their studies, a regular change in the intensity of cracks was proved both in the area and depth of the deposit.
The design of mining technology in natural stone deposits is carried out according to the average indicator of fracturing and blockiness.In the development of methods for determining the yield of facing stone blocks and justification of technologies for their extraction depending on the blockiness of the stone the following scientists were engaged at different times: M T Bakka [2,8], B P Belikov, S O Zhukov, Yu H Karasov, O I Kosolapov, V V Kaliuzhna, R V Sobolevskyi [3,4,[9][10], V V Korobiichuk [3,9,[11][12], S S Iskov [4,11], V H Levytskyi [9] and others.

Methods
There are many different classifications of cracks based on different qualification characteristics.The most suitable for facing stone massifs is the genetic classification of Bolk cracks, based on the classification features of H Cloos [1].In accordance with it, longitudinal S cracks are distinguished (the difference in the angles of the crack extension and the plane of the outcrop or slope is not more than 20°, developed along the elongation of plagioclase crystalsparallel to the structures of magma pouring during its granitization), transverse Q cracks (the difference in the angles of stretches is more than 70°, directed approximately at right angles to the longitudinal ones), D diagonal cracks (steeply falling cracks that are azimutically developed between the systems of longitudinal and transverse cracks, the difference in the angles of stretches within 21°-70°, these are chipping planes formed by compression perpendicular to the direction of the flow line), and primary reservoir L cracks.According to the magnitude of the angle of incidence, vertical (75-90°), steep (45-75°), gentle (15-45°), slightly inclined and horizontal (0-15°) cracks are distinguished.
When exploring a field, its geological and economic assessment, and conducting a pilot mining quarry, fracturing and blockiness studies are best performed using mining and geometric methods.In this case, the study is performed: • vertical and inclined crack systems -by mapping cracks in the faces of mine workings and natural outcrops, followed by drawing up plans, maps and fracturing diagrams; • primary reservoir system of cracks-mainly due to the study of the core and walls of wells, as well as in the faces of mine workings; • blockiness -for studying the core of wells and the results of monitoring the output of block products from the quarry.Method of mass measurements of cracks in stopes consists in measuring the main parameters of cracks, their instrumental binding and subsequent desk processing.When mapping cracks, their strike, dip direction and dip are measured.The disadvantages of this method are the high labor intensity of field and desk work, incomplete study of primary reservoir cracks, which does not allow us to fully draw conclusions about blockiness.The most common methods of graphical representation of cracks are their display in the form of pie charts (in particular, cracks), plans and maps of cracks.The results were processed using InnStereo beta6 and OpenStereo 0.1.2f.Study of fracturing behind the core obtained during the sinking of exploration wells of core drilling, consists in the study of the core obtained as a result of drilling: sketching natural cracks found in the core at all lifting intervals, determining the elements of their occurrence and measuring the distances between cracks (i.e., the lengths of undisturbed core columns).The disadvantage of this method is the presence of artificial cracks obtained during drilling, which are difficult to distinguish from natural ones.
The following indicators of cracking were determined for the core: • fracturing modulenumber of subgorizonal and inclined cracks by mineral resources per 1 m of well: where n -the number of sub-horizontal and inclined cracks detected in the well core; l -length of the well core by minerals, m; • specific linear fracturing -the average distance between cracks in the same system, equal to the ratio of the total length SK of all sites in the measured direction (mineral capacity along the core axis), up to the number of NK these sections (core columns) between subgorizontal cracks: These indicators are accepted as the main ones in the assessment of blockiness, classification of natural separateness by the shapes and sizes of structural blocks, classification of rock overburden by the complexity of its development, zoning of quarry field sections by structural separateness and natural fracturing, justifying the parameters of block mining technology.
The study of core fracturing allows us to estimate the theoretical yield of blocks from the array based on the percentage yield of core columns even at the exploration stage.Since only one block size can be determined from the core (the height is determined from the core axis), it is usually assumed that in all three directions the distance between the cracks is the same, and the block has a cubic shape with three equivalent edges.Therefore, the theoretical yield of blocks from the array will be directly proportional to the total sum of the lengths of core columns with a size of at least 20 cm obtained from 1 m of core, and inversely proportional to the number of such columns per 1 m of drilling.
That is, the theoretical output of blocks from the array B can be found by formula (3): where K -the yield coefficient of a block from a block stone, taking into account losses during its processing, for the Pshenychne gabbro deposit is assumed to be K = 0,33; L1 -the total length of core columns with a size of at least 20 cm per 1 m of drilling, m; nk -number of core columns larger than 20 cm per 1 m of drilling; a -core output in the form of columns with a length of at least 20 cm (%).

Results and discussion
Using method of mass measurements of cracks in stopes, cracks were found in a pilot mining quarry and their characteristics are given in table 1.
Roses-fracturing diagrams are mainly used for horizontal and gentle occurrence of rocks (when the main crack systems are steep), they allow identifing the main crack systems and estimating their spatial position and the number of cracks in 10 ° intervals, determining the average strikes of the systems.By the scale of the vectors, you can judge the number of dimensions for each system.However, these diagrams do not take into account the slope angles of the cracks, since all cracks are distributed only by strike or dip direction.On the rose-diagram, constructed for the Pshenychne gabbro deposit (figure 1), two almost mutually perpendicular crack systems are clearly distinguished: with dip directions in the intervals of 90-100 ° and 180-190°.The dips also clearly distinguish sub-horizontal (with an angle of inclination of 0-10°) and vertical and subvertical (with an angle of inclination of 80-90°) crack systems (figure 2), and the number of inclined cracks that can reduce the yield of blocks is negligible.
On pie chart fracturing, constructed, for example, using an equal-plane system Walter-Schmidt grids (figure 3 (a)) or equilateral Wolf grid, each crack is deposited according to the elements of occurrence (dip and dip direction) as coordinates.These diagrams allow us to quantify the presence of cracks in different directions, as well as compare diagrams constructed for different deposits and sections of the same field.They are easily transformed into pie charts with crack density isolines (figure 4 (b)), at which the maxima are well distinguished crack systems, common in the deposit.Angular distances between maxima allow estimating the shape of natural blocks.Pie charts of fracturing allow us to identify the following crack systems in the Pshenychne gabbro deposit: • I system is vertical steeply falling cracks with dips of 88-90°, with dip directions of 92-95 ° and strikes of 182-185 °; • II system-is vertical steeply dipping cracks with dips of 86-88°, dip directions of 182-185 ° and subvertical with strikes of 184-186 ° through 0.1-0.3 m. • L -primary reservoir (horizontal) crack system.
• Diagonal cracks with an azimuth of 30-40 ° are rare and have a length of up to 3 m.The diagrams show that the angles between the main crack systems are almost straight.The best case from the point of view of block yield is the case in which cracks form no more than three maxima, the angles between which approach 90°.This allows you to get blocks on the quarry that are close in shape to a parallelepiped.
The results of calculating of indicators of cracking, determined for the core of the Pshenychne gabbro deposit, are shown in table 2. Core drilling wells reveal mainly only horizontal and slightly inclined cracks (vertical and inclined cracks almost do not fall into the core, for example, for 11 wells of the Pshenychne gabbro deposit, only 3 cracks out of 332 (i.e.0.9%) are vertical (table 2)).Subgorizontal cracks with uneven walls and ironization along the planes were mainly found for the core, and individual IOP Publishing doi:10.1088/1755-1315/1319/1/0120096 lapped cracks were also distinguished, which had signs of ironization and chlorination.The table shows that the average distance between cracks in the deposit is 0.52 m.Plotted according to the fracturing modulus (figure 4) and specific linear fracturing (figure 5) plans in isolines show a slight increase in fracturing in the eastern part of the field.Plans were built in isolines using Surfer 15.According to the classification of rocks of M. T. Bakka by fracturing (table 3) the field is located on the border between the II (highly cracked (medium-block) and III (medium-cracked) categories.The results of calculating the theoretical yield of blocks of the Pshenychne gabbro deposit are shown in table 4, the average block rate for the field is 28.8%.The output of blocks calculated from the core practically does not change within the deposit (figure 6), which eliminates the need for its block zoning.
To determine the yield of blocks and their distribution into groups, a pilot production quarry was conducted at the field in 2019.In total, it produced 2,620 m 3 unchanged gabbro, from which 741 natural blocks with a total volume of 660.14 m 3 (25.2%)(table 5) were obtained, which fully comply with the requirements of State Standards of Ukraine DSTU B EN 1467:2007 "Building materials.Natural stone.Raw blocks.Requirements" (EN 1467:2003, IDT).
A comparison of the theoretical output values of blocks determined by different methods shows their close values with each other (table 6).The method for determining blockiness from core columns does not take into account diagonal cracks.The most reliable method is considered to be experimental mining, but its results are accurate only for the site that was studied, and similar in terms of occurrence conditions and fracturing.The actual output of blocks to the field during its industrial development is slightly lower and amounts to 20%.

Conclusions
The following main crack systems are common in the Pshenychne gabbro field: I system of vertical steeply falling cracks (dips of 88-90°, dip directions of 92-95 °, strikes of 182-185 °), II system of vertical steeply falling (dips 86-88º, dip directions 182-185º) and subvertical (strikes 184-186º), primary-reservoir (horizontal) crack system.Diagonal cracks with dip directions of 30-40 ° are rare.The angles between the main crack systems are almost straight, which makes it possible to get blocks on the quarry that are close in shape to a parallelepiped.The obtained values of the parameters of the selected crack systems can be used both for a general assessment of the main parameters of the fracturing of an array of decorative stone, and for the design of mining operations.For example, the movement of the quarry mining front should coincide or be at an angle of 90 ° to the strike of the most developed system of vertical cracks of the massif, and the separation of blocks should be carried out so that their long side coincides in direction with the dips and dip directions of this crack system [3,8,11].Therefore, for individual sections of the field, it is advisable to adjust the directions of mining operations, in particular the plane of separation of blocks from the massif, taking into account the spread of cracks [11].
The calculation of the block content for experimental mining (25.2%) and core columns (average 28.8%) gave similar results, the block value corresponds to the category of the array by fracturing according to the classification of M. T. Bakka, it is located on the border between the II (highly cracked (medium-block)) and III (medium-cracked) categories.The output of blocks calculated from the core practically does not change within the deposit (figure 6), which eliminates the need for its block zoning.Information about the content of blocks of different groups in the array allows you to predict the results of further development of the site on the block stone; data on the spatial placement and output of blocks from the array should be taken into account when choosing elements of the development system, when planning the volume of block extraction and production of block products.

Table 6 .
Comparative table of blocking indicators.