Administrative Assistant

Mariana Minerals•San Francisco, CA

40d

About The Position

Mariana Minerals is a software-first, vertically integrated minerals company on a mission to supply the critical minerals powering modern energy, AI, and defense technologies. We’re reimagining the minerals supply chain by combining deep industry expertise with advanced software, automation, and data-driven decision-making. We are seeking a highly organized and proactive Administrative Assistant to support day-to-day administrative operations across multiple locations. This role is ideal for someone early in their career who is detail-oriented, resourceful, and eager to grow within an operations or executive support function. The Administrative Assistant will provide calendar and travel coordination, expense management, on-site office support, and serve as backup to the Executive Assistant when needed. This position requires strong communication skills, flexibility, and the ability to manage competing priorities in a fast-paced environment.

Requirements

1–3 years of administrative or office support experience preferred
Strong organizational skills and attention to detail
Excellent written and verbal communication skills
Proficiency in Microsoft Office
Ability to handle confidential information with discretion
Strong time management and prioritization skills
Problem-solving mindset
Professional and service-oriented approach
Adaptability in a fast-paced environment
Team player with a positive attitude

Nice To Haves

Experience with expense management and calendar systems preferred

Responsibilities

Assist with scheduling meetings, managing calendars, and coordinating internal and external appointments
Help prepare meeting materials, agendas, and notes as needed
Support coordination of cross-functional meetings and company events
Book and manage domestic and international travel (flights, hotels, ground transportation)
Handle last-minute travel changes and troubleshoot logistical issues
Prepare and submit expense reports in a timely and accurate manner
Reconcile receipts and assist with tracking budgets or spending reports
Provide in-office support across multiple sites as needed
Coordinate office supplies, deliveries, and facilities-related requests
Assist with visitor management and on-site meeting logistics
Support internal events and team off-sites
Serve as backup to the Executive Assistant during absences
Provide overflow support during high-volume periods
Assist with special projects and ad hoc requests