In this article we examine the social determinants of CSR practices by mining firms in the territories where they exploit resources. We argue that mining firms are caught between headquarters policy on CSR, and demands emanating from locally-based societal groups. Headquarters policy provides a process-based framework for engaging with stakeholders, a menu of favoured activities, and guidance on issues of global or home-country salience. But social mobilization explains the intensity of corporate social responsibility (CSR) investments and the timing of spending. We situate the analysis within the literature on the influence of social movements on policy implementation. The empirical evidence for the paper is based on a comparative case study of the influence of activists over corporate social responsibility policy and practice in the mining sector in Chile and Argentina, using both secondary sources and primary field research.