The gold mining project is located at the south western part of Ghana. The proposed Pit A is an extension of the active mining area of the existing operations of XYZ Mine. The ore deposit comprises generally north-south trending, steeply west dipping auriferous quartz veins hosted by strongly silica and iron carbonate altered, medium to coarse grained, carbonaceous greywacke. A north-south trending dolerite dyke, dipping sub-vertically to the east cuts the depth extension of the main vein.

In the southern portion of the deposit, a west-northwest to east-southeast trending, steeply south-southeast plunging “dyke-like” granitic intrusion is cut by numerous auriferous quartz veins forming a sheeted vein system. In the north of the deposit, mineralization generally occurs in a single lode, but in the south, the mineralization occurs as two main lodes and a series of narrow stacked lodes around or in the outer margins of the granite intrusion. Current interpretation has the main mineralization event occurring post-granite intrusion and prior to intrusion of the dolerite.

The total material in bank cubic metres (bcm), which include oxide ore, fresh ore and waste to be mined over the life of the proposed pit (1 year) is estimated as 3.921 Mbcm. The pit will be mined with 6.0 m bench heights over a 3.0 m mining flitch. The deposit will be mined by conventional open pit mining methods, which will utilise open pit mining equipment as listed in Table 1. The size of the mining fleet has direct effect on the quantity of rock material planned to be blasted (or mined) over the period and the generation of infinitesimal ground vibrations to the environment. It further contributes to the atmospheric impact of mining (dust, noise) in the environment [2] .

The Kuz-Ram fragmentation model [3] [4] [5] [6] was used to assess the geometric parameters proposed for blasting at Pit A. The blast geometric parameters for Pit A have been determined for the oxide, transition and fresh rock zones of the encountered rock formations. Table 2 shows the evaluation of the proposed drill and blast parameters for Pit A based on the Kuz-Ram model.

It was known that, Pit A has similar geological properties as an adjacent active pit of mine XYZ. Due to these similarities, blast performance data obtained from the active pit was used to deduce the blast performance at Pit A. Assessment of historic blast vibration and air blast performances was carried out for the active pit. A total of 144 blasts were monitored and they indicated 85.4% conformance of ground vibration, and 90.3% conformance of air blast values compared to the Ghanaian regulatory threshold limits of 2.0 mm/s and 117 dB (L) respectively. The historic blast performance data of the active pit used as a guide for the estimations are summarized in Table 3.

The historic blast performance data shown in Table 3 indicates the maximum, minimum, and average of the measured ground vibration levels, air overpressure levels and their associated co-operative charges. The standard deviations of these measurements are further assessed. The historic blast performance data from the active pit were used to establish the site-specific constants in terms of the Rock Transmission Factors (RTF) according to the Gustaffson and the United States Bureau of Mines (USBM) models, and the air pressure referenced from atmospheric pressure (Po). The established site-specific constants for the mine are summarised in Table 4.

Ground vibrations are generated when some of the explosion energy released into the ground generates vibration waves within the rock [2] . Several formulae (relationships) are available in literature for estimating the vibration level for a given site condition, however, the relationships after Gustaffson and the USBM have been widely used [2] [7] [8] [9] . Although, the Gustaffson model was developed in Sweden and the USBM model was developed in the United States of America, according to nation-wide study in the Ghanaian mining companies [7] , they have been accepted for use in the Ghanaian mining environment. The Gustaffson model (Equation (1)) and USBM model (Equation (2)) are respectively given as:

PPV = K W D 1.5 (1)

PPV = k ( D W ) b (2)

where PPV = Peak Particle Velocity, mm/s; W = Cooperating Charge, kg/hole; D = Distance, m; and K, k, b = Rock Transmission Factors (RTF).

With the predetermined RTF values (Table 4) and the various cooperating charges, PPV levels have been estimated for various distances from the blast. The estimated PPV levels according to the USBM and Gustaffson’s models are respectively shown in Figure 1 and Figure 2. Table 5 shows the predicted PPV at the corresponding distances for the cooperating charge when blasting in the various formations at Pit A using the proposed geometric parameters.

When fragmented rock resulting from the detonation of explosive charges is transported over a greater distance than anticipated the throw is called fly rock [2] . The maximum fly rock distance for a specific charge > 0.2 kg/m³ and the boulder size are estimated according to Lundborg [10] as:

L max = 143 × d × ( q − 0.2 ) (3)

Ø = 0.1 × d 2 / 3 (4)

where L_max = Maximum Throw (m); d = Hole Diameter (ins); q = Specific Charge (kg/m³); and Ø = Boulder Diameter (cm).

Using Equation (3) the maximum fly rock distance was determined for various blast hole diameters and specific charges based on blast historical records of the Mine. The fly rock model for blasting in Pit A is presented in Figure 3. Substituting the proposed blast hole diameter and specific charges for blasting the various rock zones of the new pit in Table 2 into Equation (3) and Equation (4), the maximum fly rock distances and the associated boulder sizes have been predicted and presented in Table 6. The predicted fly rock distances for blasting the various rock zones of the pit are within the 250 m clearance buffer, and hence although the 300 m buffer neighbouring settlement is less than the established 500 m regulatory clearance buffer for surface blasting operations, the Chief Inspector of Mines could grant permit for mining pit A according to L.I.2177 [1] sub section 176 (2).

*Cooperative charges in kg/hole obtained from proposed geometric parameters.

One other major blast effect is the generation of considerable air blasts or air overpressures. Unlike ground vibration, air blast seldom causes damage to structures with the resulting associated noise causing a lot of discomfort and annoyance to neighbours. These usually give rise to community agitations [2] and unrest. The air overpressures were predicted according to Rau and Wooten [11] , given as:

L p 2 = L p 1 − 20 log r 2 r 1 − A e 1 , 2 (5)

where Lp₂ = Air Blast for various Distances, r₂; Lp₁ = Air Blast at known Distances, r₁; and Ae_1,2 = Attenuation Factor (zero in this instance, thus, worst case scenario).

With computed cooperate charges of 41.1 kg/hole (for oxides rocks), 42.4 kg/hole (for transition rocks) and 44.9 kg/hole (for fresh rocks) for blasting at Pit A (Table 2), the predicted air blast at 250 m based on the average historic cooperate charge of 53 kg/hole produces 114.7 dB (L). This is about 2% lower than the regulatory permissible limit of 117 dB (L). The air blast prediction model based on Rau and Wooten [11] , using the average historic cooperate charge of 53 kg/hole obtained from blasting operations in the active pit of the Mine adjacent to Pit A is presented in Figure 4.

The air blasts or air overpressures at a blast site may also be predicted using Ollofson [12] and Persson et al. [13] shown in Equation (6) and; Holmberg and Persson [14] shown in Equation (7). However, to convert the air blast or air overpressure from mbar to dB (L) units, the relationship in Equation (8) is used.

P = 0.7 × W 1 / 3 D (6)

P = k × 0.7 × W 1 / 3 D (7)

dB ( L ) = 20 log P P o (8)

where W = Cooperating Charge, kg/hole; D = Distance, m; k = 0.75 for Emulsion Explosives; P = Air Overpressure or Air Blast, mbar; and Po = Air Pressure from Reference Atmospheric Pressure (determined as 1.8721 × 10⁻⁸ unit less for XYZ mine site).

Using a maximum cooperating charge of 44.9 kg/hole from the proposed geometric parameters for blasting fresh rocks at Pit A, the air blast prediction model based on Ollofson [12] and Persson et al. [13] model; and Holmberg and Persson [14] model are shown in Figure 5.

The maximum predicted air blast based on the proposed blast design geometric parameters for Pit A at varying distances are shown in Table 7. It is noted that, the maximum predicted air blast at 250 m from the proposed Pit A is 114.5 dB (L). Blasting at proposed Pit A using the proposed drill and blast geometric parameters would not produce air blast values above the regulatory permissible limit of 117 dB (L).

*Cooperative charges in kg/hole obtained from proposed geometric parameters.

Air blast prediction levels at 250 m when blasting at Pit A for varying cooperate charges have been modeled and shown in Figure 6. For the range of cooperate charges (40 - 100 kg/hole), the predicted air blast levels at 250 m using Ollofson [12] and Persson et al. [13] and; Holmberg and Persson [14] models are below the regulatory threshold values of 117 dB (L) for residential community.