HPC platforms are capable of generating huge amounts of metadata about different entities including jobs, users, and files. Simple metadata, which describe the attributes of these entities (e.g., file size, name, and permissions mode), has been well recorded and used in current systems. However, only a limited amount of rich metadata, which records not only the attributes of entities but also relationships between them, are captured in current HPC systems. Rich metadata may include information from many sources, including users and applications, and must be integrated into a unified framework. Collecting, integrating, processing, and querying such a large volume of metadata pose considerable challenges for HPC systems. In this paper, we propose a rich metadata management approach that unifies metadata into one generic property graph. We argue that this approach supports not only simple metadata operations such as directory traversal and permission validation but also rich metadata operations such as provenance query and security auditing. The property graph approach provides an extensible method to store diverse metadata and presents an opportunity to leverage rapidly evolving graph storage and processing techniques.