Administrative Assistant

About Mariana Minerals

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.

The Role

We are seeking a highly organized and proactive Administrative Assistant to support day-to-day administrative operations at our Houston office. 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 administrative support to the CFO, including calendar and travel coordination and expense management, while also supporting day-to-day office operations. The role will also serve as backup to the Executive Assistant as needed. This position requires strong communication skills, flexibility, sound judgment, and the ability to manage competing priorities in a fast-paced environment.

What You’ll Do

Administrative & Calendar Support

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

Travel & Logistics

Book and manage domestic and international travel (flights, hotels, ground transportation)

Handle last-minute travel changes and troubleshoot logistical issues

Expense & Reporting Support

Prepare and submit expense reports in a timely and accurate manner

Reconcile receipts and assist with tracking budgets or spending reports

On-Site & Office Support

Provide in-office support 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

Executive Assistant Backup

Serve as backup to the Executive Assistant during absences

Provide overflow support during high-volume periods

Assist with special projects and ad hoc requests

Desired Qualifications

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

Experience with expense management and calendar systems preferred

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

Our culture is built on four principles:

Everyone Gets Home Safe. We never put speed or cost ahead of people.

Extreme Ownership. We take full responsibility for outcomes, relentlessly driving toward solutions.

Engineer Out Requirements, then Automate. We simplify, optimize, and then automate for scale.

Share Your Legos. We collaborate openly, share knowledge, and empower each other to build bigger, better solutions.

Join us as we build the future of responsible mineral sourcing and supply!