Magnesium (Mg) isotopic composition of sedimentary silicate fractions provides key critical constraints on the history of silicate weathering and climate evolution. Since sedimentary rocks typically contain authigenic carbonates, standard whole-rock digestion co-dissolves both carbonate and silicate phases, resulting in hybridized Mg isotope signals. Accurate analysis therefore requires separation of silicate components through selective dissolution methods that exclude Mg from carbonates. However, standardized dissolution methods specifically designed for Mg isotope analysis of the silicate phase in sedimentary rocks are still lacking. Significant variations exist among different pretreatment protocols, particularly in the choice of leaching reagents and cleaning procedures. And the Mg isotope fractionation behavior of silicate phases under different acid reagents and leaching procedures remains unclear. In particular, the effects of strong acids on silicate components and the potential extent of induced fractionation are not well constrained. This issue becomes notably critical in studies requiring high-precision Mg isotope analysis. In this investigation, we have systematically designed and performed chemical leaching experiments on Marinoan diamictites from South China to develop an optimized and robust leaching pretreatment scheme for Mg isotope studies of clastic silicate fractions. Our results demonstrate that 0.5 mol·L-1 Acetic acid (HAc) exhibits limited efficiency in leaching poorly soluble carbonate minerals (e.g., siderite), as shown by only 7.7% and 1.4% decreases in the leached residue's Mg/Al and Fe/Al ratios relative to the whole-rock values. For samples containing Mg-rich and Fe-rich carbonates, 0.4 mol·L-1 hydrochloric acid (HCl) is recommended to ensure efficient carbonate removal and subsequent reliable acquisition of silicate Mg isotope signatures. This study provides the essential experimental basis for developing sedimentary Mg isotopes as a quantitative paleoenvironmental proxy, thereby enabling more refined reconstructions of Earth's surface evolution.