Application of Micron Shear Mill in the Processing and Preparation of Coarse Gold-Bearing Samples from Carlin-Type Gold Deposits

Gold in ores primarily occurs as native gold and can be classified by particle size into five categories: micro-grained, fine-grained, medium-grained, coarse-grained, and mega-grained. Among these, native gold particles observable by the naked eye or a microscope are also referred to as visible gold. Native gold exhibits high ductility and cannot be crushed synchronously with the ore. Mega-grained, coarse-grained, and medium-grained gold particles easily lead to uneven sample preparation and poor repeatability of analytical results. This seriously restricts the accuracy of gold analysis and the precise evaluation of resources, posing a major challenge in gold ore sample preparation and analysis. In this study, an innovative sample preparation process is proposed. Based on the traditional process, a micron shear mill was used for wet grinding, followed by filtration, drying, and homogenization. characterization was performed using chemical analysis, artificial heavy mineral separation, and scanning electron microscopy (SEM). The experimental results showed that, compared with the traditional process, the proposed process offered the following advantages: (1) The relative standard deviation (RSD) of gold content determination decreased from 8.13%–18.92% to 2.80%–4.08%, indicating significantly improved precision. (2) Artificial heavy mineral separation revealed that the total number of visible gold particles in the prepared samples decreased from 2000–3000 to 76–335. Among them, the proportion of coarse gold decreased from 3%–11% to below 0.90%; the proportion of medium-grained gold changed from 15%–45% to 9.55%–80.26%; and the proportion of fine- and micro-grained gold changed from 53%–72% to 19.74%–89.55%. The maximum dimension of native gold decreased from 0.54 mm to 0.25 mm. (3) SEM observations showed that gold particles processed by the traditional process exhibited numerous surface scratches and irregular surfaces. In contrast, those prepared by the proposed process were regularly spherical with smooth surfaces and well-defined cross-sections. This study reveals that the key mechanisms for achieving efficient crushing of coarse gold-bearing ores are the shear force introduced by the shear mill, the liberation of native gold particles of medium and larger sizes, and the reduction in aspect ratio and uniform dispersion of medium-grained gold in the prepared samples. The innovative process based on the micron shear mill effectively addresses the problem of uneven sample preparation for ores containing coarse gold particles and provides reliable technical support for the accurate evaluation of gold resources.